The Bloody Invaluable Book has this to say on the planet of Golgafrincham:

It was, the book says, the most marvellous, the most artistic, the most culturally evolved of all planets. It had art, poetry and prose which made lesser planets weep, mostly due to its inspiring mountain ranges, its myriad flowers, and its general breath taking beauty. But, as art marched along, so did industry and commerce. Within a century, Golgafrincham was a mess of steel, glass and other business-like materials, as they amassed in beautiful cities to produce beautiful business mergers and run the beautiful stock exchange. However, with all this jaw-droppingly beautiful business and commerce, the people, as a whole, lost their edge for creative arts. When there was a creative renaissance, it was no longer placed at the hands of those who had studied and practiced for years upon years; anyone who wanted to be an artist could. And it wasn't until it was too late that they realised this was not necessarily a good idea.

What was a good idea, they decided, was to rid themselves of this problematic faction of their society. These were people who were not skilled at arts or commerce, but really, honestly believed not only that they were, but that they could have done better than the people in charge. Thus, an idea was formed. The heads of the art world combined with the heads of the business world, who in turn outsourced to the every day workers, and as such a story was told. A story so subtle, so believable, and so utterly false, that as it was spread and retold, it changed into the spoken word equivalent of a hydra. Documented interpretations include "the planet was about to be eaten by a giant star-goat", "The planet is going to turn itself inside out", "The planet is about to be sucked into a black hole", "Croatoan virus" and "someone opened a container of ancient evil without reading the manual first". When a massive web of lies and falsehoods concerning the planet's imminent doom was in place, the useless "we could do better" faction were bundled into a ship and told that it was a far, far greater thing they did now than anyone had ever done, and weren't they lucky to be given a chance.

Once the ship had left, the people of Golgafrincham rejoiced in the knowledge that they could safely visit an art gallery, or watch a political debate, or browse the internet without being confronted by hacks, trolls or half-assers. Then, unfortunately (and, writers of the Bloody Invaluable Book are legally bound to say, entirely unconnected to the initiation of the Impala's Leap of Faith drive over the planet's atmosphere), an archaeologist opened a container of ancient evil without first reading an instruction manual, which released the Croatoan virus and turned the planet inside out, before summoning from the void of space a giant star-goat which promptly ate the planet before ejecting it into a black hole. At last report, the goat is still fine.

(-*-)

Groaning, weary creatures pulled themselves out of the primordial swamp, gasping and struggling as their lungs took in the unfamiliar atmosphere. The primitive jungle planet accepted the new life wordlessly. The current occupants scattered quietly across the planet, few knew of the event. Slime spread across their faces, writhing in agony as they acclimatised themselves to forces such as gravity and friction, the new life fell slumped on the virgin grass.

"I really hope I saved file before we crashed…"

(-*-)

After the Golgafrincham ark ship crashed, Dean and Castiel made their excuses and left the survivors to it. They decided their time would be much better spent ignoring the raving loonies and exploring this strange new planet, which stretched out before them in untouched, natural beauty. Castiel said he had a feeling the continents were still shifting, but that may have been the effects of the pills he took from the Golgafrincham medical bay.

The ultimate end goal was to find somewhere that Castiel's SOS device would get enough signal to send out a beacon, but Dean wasn't too worried about being thrown all over space any time soon. After possibly the most manic time of his life (he still wasn't sure he'd only been in space for twenty four hours, regardless of what his watch said), he was happy to explore this strange yet oddly familiar planet and pretend he was Indiana Jones for a while. A while was, at his last estimation, about a year and a half.

They had picked west, as a direction, and when they ran out of land they started walking down the coast. Food and water were plentiful enough, if they were careful, and they were helped along by the indigenous, ape-like natives who would often leave fruits and berries for them which were safe to eat, before quietly shuffling back into the small huts and shelters they lived in. From their body language it was clear; Dean and Cas only got food on the understanding that there was no further interaction. It was a sort of pre-emptive peace offering. They had noticed, though, as they travelled, decidedly fewer and fewer of the primitive natives, and decidedly more and more of the Golgafrinchams. The shift in population seemed oddly ominous to Castiel, and naggingly familiar to Dean.

"Shit…" Castiel sighed, as they trekked up a hill, for no reason other than that it was there. "This is like the detox course from hell…"

"Yeah, exercise will do that to you." Dean stopped for a moment, stretching his tired muscles. He reached into the pockets of his tattered and mud-stained trousers and took out two of Castiel's empty pill bottles which were now serving as water bottles as Cas didn't trust Dean to tan and clean an animal bladder drinking pouch. Actually, they had yet to hunt or kill their own meat, often being left some by the quiet, hut-dwelling natives, so issues of what to do with the hide or offal was irrelevant.

"Come on, we're nearly at the top of the hill."

"What's at the top of the hill?"

"I have no idea. Probably a stunningly beautiful view."

"Oh." Castiel sighed. "Another one of those."

"Come on." Dean slapped Castiel's arm, smiling at him. "We can do some yoga when we're up there. That's what you were going on about at that community centre, right? 'Lands untouched by human hands, imagine your spirit centre' and all that crap?"

Castiel started walking behind him, slight guilt troubling his features.

"Actually, since we're stuck here and we probably will be for a while, I guess I should maybe tell you about that… What I taught everyone in that class wasn't yoga."

"It wasn't? Sure looked like yoga…"

"No. It was… it was the ancient mating ritual of my people."

Dean stopped walking for a moment, stared at Cas, realised he was being serious, and then carried on walking.

"Oh." He said.

"Yes… it's to do with flexibility and fitness, to exemplify who would be most fulfilling as a partner."

"Huh." He said. "Well, I guess that explains why you made a pass at me, if I was a potential mate."

"No, I made a pass at you because I thought you were attractive. I was sad you didn't come back because you were a potential mate."

"Ah. Well, hey, for what it's worth, if I hadn't been with Lisa… or had a massive bout of food poisoning, I probably would have."

"Good to know." Castiel said, as they reached the crest of the hill. Dean had been right; it was another frankly flabbergasting view. Grassy, wooded hills and valleys stretched out around them before fading down towards the sea. The human and the betelgeusian stood there, letting the breathtaking view do its job and take their breath away.

"Dean?" Castiel asked, not quite managing to tear his eyes away from the view.

"Yeah?"

"When you said 'you would have', was that about coming back or about taking me up on that pass I made at you?"

Dean raised an eyebrow at Cas, scratching at the thick beard he had gotten (Cas had mocked him for his human hairiness; apparently aliens can grow hair only if they choose to).

"Well, I'm not with Lisa, and I don't have food poisoning. And before Earth ended, I was not intending to take up Yoga, legit or not."

"Huh." Cas nodded. "So… you wouldn't say no, if I asked?"

Dean thought.

"No."

"Oh."

Then, Dean found himself suddenly with his mouth full of someone else's tongue, and was not entirely unhappy with the situation. His feelings towards it only improved when he felt Castiel's hands wrapping around him, fumbling to rid them both of the shredded, stained vestiges of clothes that they still wore.

"You don't mess around, huh?" Dean laughed, as he let Castiel pull him to the ground. Cas was already on his back, his hands trailing over Dean's chest.

"The amount of wormholes, time travel and cryochambers I've been through… I did the math, it translates to something like five earth years since I've had a good lay."

"Wow." Dean muttered, trailing his lips across Castiel's neck, glancing down to note that, at least anatomically, humans and betelgeusians weren't all that different. "So, no pressure."

"Just hurry up." Castiel grunted, pulling Dean closer.

The presence of such a personal scene in the otherwise quite impersonal chronicling of Dean Winchester's life may seem gratuitous to some; this is, after all, the story of 'The Bloody Invaluable Book: Lightyears of Entertainment' and, while the Book has many things to say on the subject of sex (see pages 2, 7, 9, 39, 66-67, 69, 99, 100 through to 700 inclusive, 3,000, 3,950 and pretty much the rest of the book), the sexual intercourses between Dean and Castiel may not instantly be seen as important to such a story. The unknowing reader could very easily make the assumption that such a scene was only included to promote further interest, as the trifling matters of physical relationships have rarely, if ever, produced anything of cosmic importance.

This assumption is, however, very wrong, as Castiel is about to find out.

"Oh god…" He groaned, writhing under Dean. His back arched as he stared out at the beautiful (if upside-down) view of sweeping valleys, domed hills and paths of rivers, fault lines and natural erosion that stretched between them. "Oh god…"

"That's right." Dean muttered, enjoying himself rather a lot, as is to be expected.

"Oh my God! Dean!"

"Yeah that's…"

"No, Dean, look!" Castiel pointed, before shoving Dean off him and flipping over onto his front. He was crouched down, staring into the distance and creeping Dean out a little bit.

"Cas, if you wanted to change positions…"

"No, Dean, look!" Castiel grabbed Dean's arm and pulled him down so he was crouching exactly where Castiel had been, moments before. "Can you see it?"

Dean saw it. And he had no idea how to react.

It was, from a certain angle, the sight that told them not only what planet they were on, but exactly how much of a problem they had on their hands. There, spread across the prehistoric hills of San Francisco through the use of meandering streams, fault lines and natural erosion, was the signature of one 'ShurleyBurlfast'.

"Shit." Dean said, because he really didn't know what else to say. "So this is… Earth."

"We're on Earth. Earth from about sixty million years before the end, maybe, but Earth none the less."

"But that means the natives… the Neanderthals, I guess… they're dying out. We have to help them?"

"Why?" Castiel sat back, running a hand over his face. "No point. The Golgafrinchams are here now."

"But, if they die out…"

"Face it, Dean. The quiet, understanding, simple creatures aren't the ones you evolved from. The bunch of wannabe politicians who we left because they were actually trying to reinvent the wheel? Those are your ancestors."

"But… But… no. No, that can't be right."

"It is."

"Society, my society can't come from that."

"It can, Dean. Because we've seen it. We've both seen it, we've both been there, and we know how it'll end."

"But…" Dean trailed off, before throwing himself back on the grass and covering his face with his hands. "Shit. I mean… so it's all for nothing, right? Even the whole meaning of life computer matrix stuff, it doesn't even matter. Since they've turned up, they've messed with it. The ultimate question is going to die with the Neanderthals who can't tell anyone."

"Yeah." Castiel sighed. Then, he sat up straight and stared at Dean. "No… wait, it's possible… you might not have the right question, but you might have a mutation of it. A variant. If we could find some way to look into your subconscious…"

"What's the point?" Dean sighed, staring up at the sky.

"No, that doesn't fit. 'What's the point?' 'Yellow'. Try again."

"No, Cas, I mean… the answer is "Yellow". Whatever the hell the question was, it's not something I'm going to be able to figure out here and now."

"No, come on." Castiel grabbed his clothes and started pulling them on as he stumbled down the hill. Reluctantly, Dean followed him.

And so it resulted that Dean did not finish having sex with Castiel on top of a hill in prehistoric San Francisco (a fact that annoyed him rather a lot), but instead ended up sat in a cave somewhere, with Castiel holding piles of dried leaves in his bundled up shirt. Dean had written letters on each leaf until he felt like he'd done enough, and now Dean was supposed to pull them out without looking.

"This is stupid."

"Just… humour me. Go on."

"Fine… The first letter is… W."

"Right. Put it down on the floor."

"Next… H, A, T…"

"'What'! It's working!"

"C, O, L, O."

"Or maybe not…"

"U, R, I, S."

"Uris. Is it Latin? Colo Uris… Oh! What Colour Is! It is working, it's just spelled in queen's English. Keep going."

"T, H, E… Cas, can you not grab my ass?"

"Sorry. It's getting exciting."

"M, O, S, T, L, I, K, E, L, Y… Most likely."

"What colour is the most likely…"

"T, O, G, R, E, E, T…"

"To greet…"

"Y, O, U."

"You. 'What colour is the most likely to greet you…' well? Keep going!"

"That's it."

"That's it?"

"No more letters."

Castiel blinked down at the lines of leaves on the floor.

"What colour is the most likely to greet you? Yellow."

"I think I got that in a joke book from my uncle when I was five."

"I don't get it."

"You know, it sounds like "hello"."

"No, not that. I mean… all that for a really bad joke?"

"Eh." Dean shrugged. "I always thought whoever ran the universe must have a messed up sense of humour."

Cas laughed. Dean laughed. They ended up laughing so much that they fell over, and sat gasping for breath on the floor.

"Oh, man." Dean said, kicking the leaves aside as he stumbled to his feet. "C'mon, let's go get some food."

And they did. They looked out over the untouched, undeveloped but ultimately doomed landscape of prehistoric Earth, and they saw that is was good. And, in considering the six million years the planet had left, they realised that maybe finding the question didn't matter so much after all.