A fun old article from the 90's of quake. Worth a read if you want.
LinkAlso. Haven't read through this stuff in a long time, but if you like to see some of cool things that are doable, in comparison to what people use, take a read through some of it. Each of the different tuts has a .map attached, and some have a .bsp. Most of it has been said before, but I haven't seen this much of it in a while. Would love to transfer over some of the relevant tuts to the wiki here and format it correctly (I'm a documentation creep).
Func/Target/Trigger/Misc: Everything on ents that available in original q2.
Construction Tips: Pretty much everything you could ever need from lighting, to hint brushing, to logic gates.
Yada yada no one cares yada.