In fact, Tom, this maps was already ported to tremulous using a decompilation/recompilation process, and it was very wrong.
There wer plenty issues like missing textures (you see the void at some place), or some geometric faces misplaced (with clip issues), the lighting is completely wrong since it has to be redone and the guy who redone it was not as good as the author (and I will not be as good as the author).
Yes, the first time I've seen this map was this crappy tremulous port, I said, « wow, it looks so nice for a tremulous map », then I tried the UrbanTerror one and I said « wow, the tremulous port was so ugly ». Currently, I think a decompilation/recompilation is a port done wrong.
And a funny thing, tremulous-gpp and tremfusion were not able to load this tremulous port out of the box, only Unvanquished, it means some things were wrong in the map.
Unless the engine use another map format, the best way is to modify things inside the bsp directly and in texture/shaders.
Doing that, you will not be able to change geometry of the map, but you can change many things: you can place buildings (spawn points, turrets, overmind etc.) where you want if you know how to modify it in the bsp, you can substitute or rework some shaders, and I'm working to be able to change some surfaceparms with my tools (I have to check if it works). Also, you can tweak the lighting (adjusting luminosity, contrast, gamma or color atmosphere) using a simple picture tool once you know how to export and reimport lightmaps.
You can't get a complete .map from a .bsp, for example, the lights are compiled to lightmaps that are texture files, unless I'm missing something, you can't roll back this part.
So, this map loads very well in Unvanquished, and is already playable unless a minor bug I have to fix: a place in the map is not buildable and it's a part I've not yet tried to modify with my tools.
I can't change the geometry of the map, but it's not a big issue, there is some places where a tyrant can't go, like a cubbyhole, but if a human puts a telenode in it, he will not be able to protect it and even a advanced marauder can zap it from outside. It's not a map done with Unvanquished in mind, so do not expect to not have some gameplay issue at all, but it can be fun to play and it is refreshing.