I actually had one of these[1] which I laid out as a 3D unicursal labyrinth looping over and under and roundand round from the entrance to the heart, everything either wall (minimal, possible sandstone/whatever workaday rock block I had easily at hand), corridor (trapped, eventually) or the outer ramps (probably limestone, except for the electrum tip, if I remember my borrowed design philosophy correctly).
The designing was more fun than the actual building, and it was probably never used properly (a kobald-confuser, possibly) before ordinary concerns of the 'support fortress' got hit by my mismanagement. Or inability to handle the inevtable siege. But many a lost civilisation leaves behind structures of strange and confounding purpose, and possibly somewhere buried in some long lost zipfile I have a v0.31ish savefile still with it awaiting someone more knowledgable about the gameplay to go back in and recover/reclaim whatever failure mode I left it in and do a proper job of making it useful. (It's a philosophical question whether a world that is never run again is perhaps 'awaiting', but perhaps by telling my tale to someone else, the memetic seed might pass onwards yet...)
[1] Actually, I had others, like the pyramids/obelisks I dug out of bedrock, the only things I actually built were the bridges leading between the 'upper' levels and the wall I built around the edge to stop anything nasty looking down into my wondrous excavation frm the edge of the map. But the insides (and underneathh) were rather boring additional access tunnels on an underlying grid at the bottom-most diggable layer (pre-Magma Sea cavern layering).