Once upon a time, I used to be a fairly active amateur level designer, doing my thing for various engines based off the venerable Quake engine. I've been out of it ever since I shut down the old Valve Developer Union site I ran and the Quake scene got sick of me, but here we are.
All of these should run fine in a vanilla engine. Still, for my Quake sessions, I prefer Mark V, a modern engine with support for software rendering for that extra crispy look. Sources included; feel free to do whatever.
"Temple of the Strange"