"An honorable establishment this is not, and yet, some of these lowlifes aren’t evil. In fact, all but a few pray on monsters in dungeons, rather than well guarded cities." In game description.
Thieves' Guild is in the same location in Outer Terra as Fierce Fold/Dripstone is found in Taskmaker, but the map layout is totally different. You can reach it from the South by cutting through the mountains, or from the North by taking a ship from Zehner's Palace across the lake, or by using the teleport room in Castle Hall. In all three cases you will appear near the southwest corner of the map.
Angel: there does not appear to be an angel in Thieves' Guild.