Auyán-tepui is a real life geological structure located in the state of Bolívar in Venezuela. With 'tepui' meaning a tabletop mountain, it's the site of Angel Falls, the world's tallest waterfall (above sea level at least).
Within the Ragnarök Chronicles, this mountain provides the destinations for Rodriguez DiMaggio's tour-guiding service. Unbeknownst to him, his employees or the tourists however it also holds an ancient secret, that within the forest atop it and descending into its rocky heart (part of it going to the very core of the planet in fact) is an alien temple housing the Iadun, an archway which can using a similar principle to a pulse hyperdrive.
Usually the temple is hidden behind a shield which prevents any outsiders from noticing it, but when viewed it can be appreciated to, on the surface at least, exist on a raised platform that extends horizontally in regular steps until its reaches its maximum width before mirroring itself, retracting in steps the same way. At the points of maximum width and height long slices of stone stick out further, pointing in the cardinal directions, and upon each of these stands a great column, twice as tall as a house. Resting on top of these columns are interlacing beams forming an octagonal ring. In the centre of the raised platform is a stone cube building with dimensions of around twenty-five feet. Rising from the roof of this cube is a further column ascending far into the sky.
As for the interior, the walls are covered in pictographs within broad overlapping circles, while most surfaces have been partially taken over by thick green vines. The first chamber is largely empty, with simply a triangular-prism-shaped altar in the centre through whose grates you can see down into the depths below, yet beyond this you can find thin staircases curving down into the lower levels, branching off onto bridges leading to platforms at the heart of the temple surrounded by rows of seats like a Victorian operating theatre, the first of which holds the Iadun itself.