He finds a landmark

Mark looked about in awe. He knew he must be dreaming... there was no other explanation for what he was seeing. But what a dream! Everything looked and sounded so real. Not just that, it smelled and sounded real too, the cool clammy air of the cave causing the hairs on his forearms and neck to tingle.

Drawn by the sound of running water, Mark moved towards the left of the cavern where he found a small, almost hidden alcove, inside which was an ornate fountain, the glowing waters cascading down over a statue of several strange figures. There were humans, a warrior, a noblewoman or perhaps a princess, but also monsters. Half humanoid abominations he did not recognise. He inspected them more carefully, noting that the basin at the bottom of the fountain was separated into different vessels, each collecting the water beneath a specific icon.

The more he looked at it, the more he felt compelled to drink, moving forward and cupping his hands together to collect a mouthful before drinking it down. He immediately felt strange, his vision blurring as his entire body tingled and he staggered away from the fountain, temporarily blinded. Little did Mark know that he was undergoing significant changes, his body reshaping itself to resemble the figure from which he drank, his mind beginning to fog with the ideas and desires held by the icon of his choice.