Sherlock-is-sonic-in-enochian prompted: "Sherlock is an insomniac and has never felt so alone and bored in his life. What does he do with his free night-time?"
He was bored.
Not that this was an unusual occurrence, but that didn't make the experience any more enjoyable.
Even when he was bored, his mind was racing, but it was filled with absolutely nothing. The kind of nothing that was almost white noise, but with enough regularities that it kept him from seeking the solace of sleep. He couldn't sleep, very rarely could.
It was something he had discovered at a young age, and his mother and teachers had always fretted over the dark circles that were a constant under his eyes.
When describing the features of one Sherlock Holmes, there were certain traits that were always mentioned. People liked his eyes, and as he grew older, his cheekbones became very pronounced. He'd been described as looking half-starved more times than he could count. Not that it mattered, for as stunning as his eyes were, or as sharp as his cheekbones, they were always marred by the purple and grew crescents that were framed by the aforementioned facial features.
He could be exhausted beyond belief, his body could feel like it would collapse at any moment, but his mind would refuse to quiet and thus he would lie in bed, wishing for nothing else in the world than to succumb to sweet unconsciousness - but his wishes were so very rarely fulfilled.
As a child, he would lie on his back in his bed, Redbeard lying at his feet, snoring, and just stare at the ceiling. He would blink, but his eyes would always open.
It was tiresome.
Occasionally he managed to get a few hours in, and those were wonderful nights. The rare periods of rest never lasted long, but each and every moment was treasured.
Eventually he had grown out of the habit of wishing for sleep to come. There were nights where the chance of sleep was ever so tempting, and sometimes his body's need for sleep would win in the battle against his subconscious.
He had always been able to tell when that wouldn't be so, and around the age of twelve he had decided to start to make use of the time. He used to read books; stories and poems. Eventually, he had gone through all the books in his bedroom, and started to take works of nonfiction from his father's study.
His vast knowledge came more from that than anything else.
But he was a quick reader, and eventually he ran out of books to read - and as such the experiments started. He had never once thought of waking his parents in search of entertainment, but there were nights that Mycrofts' aid was needed.
It hadn't even crossed Sherlock's mind how late it was the first time it happened. All he knew was that he needed Mycroft to hold the wire and measure how far the bead went up the tube, because he couldn't do that and write everything down at the same time.
As amazing as his memory was, it wasn't yet perfect.
Mycroft has whacked him over the head with a nearby umbrella the moment he saw what was waking him up.
Sherlock never tried again, and abandoned the experiment in lieu of trying to strengthen his memory.
And thus the mind palace was born.
Months were spent on perfecting it. He had filled so many journals with words describing how it would look in the end. And once he had the plans laid out just so, he started to build it. It took him months to lay out the groundwork, and the details would only change and grow for the rest of his years.
He had it all laid out in his head, and then he worked on putting it into action.
It was surprisingly simple.
The most difficult part of the process was starting it; anyone can picture a room in their head, but a mind palace is a room in which you can interact with.
And Sherlock has mastered the art of interacting with his mind palace very quickly; after all, he did have hours and hours to devote to it.
He wasn't a very social child, and that did not change much through life. He had opened up his heart more times than he was willing to admit, and had been disappointed every time.
Until he met John.
He still couldn't sleep, and he was still bored out of his mind so very often - but he was no longer lonely.
He had had roommates before, but they were never able to get rid of the pervading feeling of loneliness he was so often surrounded with. John didn't even sleep on the same floor, but his presence itself was comforting.
He could lie on the sofa, knowing that no sleep was to come that night, and he would think. His mind would so very often race over a large variety of topics. He would spend time looking over the memories he had hoarded over his lifetime, but to achieve a nice level of calm, he would direct himself over to the room with 'John' marked on the door and simply sit in peaceful quiet, not asleep, but his mind no longer racing.
It was in this fashion that hours would pass.
He was still bored, and while John might not physically be there next to him, John made it bearable.