Heroic Maps has released a collection of Dungeon Entrances. You gotta start somewhere.
From the release:
Dungeon Entrances is a geomorphic set, comprising 4 10×10 square battlemaps which can be arranged in multiple layouts. Each tile features corridors and rooms in a dungeon setting with a different style of entrance – large grand doors, broken walls, sunken courtyards and more.
Also included is a set of 300dpi full size jpgs, for poster printing or VTT, in both gridded and non-gridded versions. (n.b. gridless version only available as full jpeg)