Knightfall, there are a lot of interesting worldmaps playable for C3C in the map forum of CFC. The size of these maps varies from 362 x362 downwards. Bigger maps can trigger huge interturn times and additionally tons of micromanagement in the turn of the player.
A very interesting worldmap, that also keeps an own mod in its files, is the Giant Earth map (I think size 256x256), that you can find here:
https://forums.civfanatics.com/threads/giant-earth-concept-map-256x256.492450/
Good to play are 180 x180 worldmaps. I converted such a
worldmap created by Kal-El, so it can be played with the C3C mod RARR (here please don´t play the Celts). All these maps have their own starting locations for the civs. There exist a lot of other interesting worldmaps, that can be played with C3C. Please have a look at the
CFC Civ 3 map forum.