To Frisk's surprise, the interior of the cave was warm. She had expected it to be freezing due to the strong wind and the snow raging outside of it, but as Papyrus and little M.K. lead her deeper, she found the atmosphere to be strangely humid. As they progressed along the tunnels, she understood why: before her appeared several large ponds of steaming water. These, as she remembered, were called thermal sources, and their presence warmed up the caverns they were progressing into. They made sure, however, to stay quiet while doing so; in the pleasant water were resting several monsters. Most of them seemed to be napping, and thus the little trio made its way without a noise, which reassured the human girl.
They then arrived to a tunnel from which emanated a faint orange light at its end. Her two new monster friends went through it and she followed them. At the end of the tunnel, she was amazed to see where the light came from. At the exit, the earth opened its mouth to give birth to a gigantic and profound hole, in the bottom of which seemed to circulate a lazy river of lava.
An unsteady bridge crossed the hole, and the two monsters joyfully started to walk on it, with some mysterious duty waiting them on the other side. Frisk followed again, but took a moment to look beneath her, amazed by that force of nature she never thought she'd one day see. She gazed upon the magnificent stream for so long that M.K. came up to her to see if she was fine. She answered that she was simply curious.
-"Oh! Well, you see, there's a lot of lava under the Isle, and Doctor Alphys helped putting in place a big machine that goes deep under the ground to take the heat and turn it into electricity! Man, it's so awesome!"
And then M.K. noticed that Papyrus had already reached the other side, so he left Frisk to her contemplation, running after his friend. The girl then left as well, not wanting to be alone among monsters that would show her no mercy.
On the other side of the bridge was an exit from the warm caverns, but, to her surprise, it didn't quite lead outside. Instead, they ended up in long and large made partly of glass and metal. There were doors at every ten meters, which all were entrances to houses, Papyrus told Frisk. The large windows on the walls allowed the girl to peek outside and catch a glance at the natural chaos. The blizzard was so strong, she could only see a cloud of white and snowflakes, all of which plunged into the night. Sometimes, she could barely spot the shadow of a tree or a rock, but each time, they faded away again, erased by the wind's wrath.
Papyrus then stopped in front of a door and entered it, M.K. staying close and inviting Frisk in. She went through the door and found behind it a cozy living room, but without Toriel's place's charm. There was no fireplace, nor smell of pies, but there was a large and comfortable looking couch placed in front of a low table on which laid several snow globes containing silly figurines.
-"Well, I guess you can sleep on the couch. Let me go get some sheets for you. And as for you," Papyrus said while looking at M.K. "go to bed. We've got a big day tomorrow!"
M.K. did as he was asked and went into another room, presumably his own. Papyrus left to another, but then came back with sheets that he gave their guest, just as promised. He was then off to sleep as well. Frisk installed herself into the large couch and prepared herself to sleep, but as she was starting to drowse, she remembered about Gaster and sat on the couch, seized the heart locket with her hand, closed her eyes and concentrated.
Before long, everything around her turned black and Gaster appeared. He smiled at her.
-"Ah! It is good to finally be able to talk normally!" he said.
-"Sir it's good to see you again! But I was wondering… What happened out there? How is there so much snow in fall?" the girl asked.
-"Remember the storm surrounding the Isle? Well, over the years, it grew so strong and unstable that it causes weather anomalies within the Isle itself. In this particular area, it mainly consists of terrible blizzards, but there are other oddities. In some places, there are strong electrical thunderstorms, in others, suffocating droughts or gravity disturbances. There is even a lake that floats!"
Frisk knew that these phenomenons were terrible to those who lived them, but couldn't help but feel impressed.
-"You were lucky, dear, to find those two naïve monsters to guide you here. It will make the task much easier!"
-"Where do we go next, sir?"
-"Well, first of all, you need sleep. In the morning, I'll guide you through this town, Snowdin, and we'll go to-"
He interrupted himself and looked over his shoulder.
-"Hmm, we've got company."
He then vanished and the room reappeared. In the dark, Frisk saw M.K. come out of his room and come to the couch. He climbed on it and sat in front of her.
-"Yo!" He started, whispering. "I can't sleep 'cause tomorrow, I'm going to the Waterfall lake! I'm gonna try and see Undyne fight! She's the coolest, I'm so excited! Man…you should totally tag along or you're gonna miss something!"
Say yes, Gaster told her.
-"Hum, yeah, sure!" she answered.
-"Great! See ya in the morning!" he said, before going back to bed.
Frisk laid on the couch, and as she closed her eyes, all she could hear was Gaster saying:
Well, this promises to be interesting.
She fell asleep.