This is addond comes with the old City update. It consists of a series of platforms connected by Teleporters, overlooking the Old City. Teleporters are in fact the main features in this floating island map styple.

There's a giant Penetrator railgun aiming a pulsing beam of energy at a huge spacecraft in the sky.

Nice DLC overall, adds some replayability to the game.

Sanctum: Slums is a new map which gimmick is teleporters, it's baseically a series of floating island connected by teleporters, there are some narrow part which the Penetrator would be good, there is also a Penetrator railgun on the map which is nice I guess. All and all, a so-so map but more Sanctum is always a good thing. Note: if you are wondering you just get a key to enter into your steam client to unlock the DLC.

As a DLC map it's pretty good. It offers enough variations from the normal maps to make it worth your while and for 0.50 (sale price) it's really good bang for your buck.

This map is a bit chaotic, and it should make for an intense fighting experience. Be sure to place a few teleports here. (Of course, you can also try to simply jump around a lot, but then you are quite likely to fall down. :-))

Creating choke-points is both challenging and rewarding on this map, so it's a good addition to the base game, if you got bored with the basic maps.