Heavily inspired by What Goes Up (M1). There is some texture alignment needed, and the bobs can be seriously annoying in net play, but this is a pretty well thought-out map. Most areas are vulnerable from multiple directions, and there are very few (if any) resting places. Keep an eye out for secrets... some of them can make inter-area travel much easier. Update aligns most of the misaligned textures.
A bunch of Marathon players took 54 of their favorite small maps, edited them a bit to their liking (more ammo, lower ledges in some cases, etc.), and stuffed them into a single Map file, to make net play easier. Unfortunately, the documentation is a bit sparse... (hard to tell which map comes from where, or what was done to it). If you're looking for a large collection of maps that someone else has already said is above average, download this.