"Borderworld Hole" is a short Quake level that I created to learn the Trenchbroom level editor.
It features a stream-of-consciousness design consisting of whatever themes I wanted to explore in a given moment. You spend the first half of the level exploring twisted hallways that periodically reconvene at the same rocky pit, but the second half ends in a hectic battle in a massive outdoor arena.
You can download the level here. Place the ah01.bsp and ah01.lit file in your game's id1/maps directory, and after selecting a difficulty level, type "map ah01" in the game's console to play it.
The map DOES NOT render properly in Quake's original engine. You have to play it using a modern source port - I most recommend Quakespasm.