Are there premade campaigns/adventures that take place at least partially in Sigil - City of Doors and where can I find them?
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Since you are interested in older stuff, here's the list of the official published adventures for Planescape:
Don't know if 4ed changed the concept of Sigil, though, or if there is a fan conversion. The only conversion I know of is for 3/3.5.
Spoilers, of course.
Expedition on the Demonweb Pits is a planar campaign for D&D 3.5 featuring Sigil in its role of extraplanar crossroad.
The PCs arrive there after a poor hook they might entirely disregard and then they need to get in touch with severla NPCs living in Sigil. A great part of the adventure happens in planes that can be reached from there but the quest-giver NPC lives in a inn in Sigil so the players will be back for restocking and talking to him quite often. The book completely ignores factions, the lady of pain and any other planescape reference that I could recognize. Such a pity.
The epic level adventure E1: Death's Reach from WotC has a (short) section based in Sigil