Originally posted by The Last Conformist
I think he's talking about the Winter terrain set.
If so, simply chose "Play Scenario" (or whatever it's called in PTW) and start the "Winter Terrain" bix.
To use them in C3C, you'll have to make a scen with "..\..\CIV3PTW\Extras\Winter Terrain" in the Scenario Search Folders textbox under scenario properties (don't change anything else). Volcanoes and Marshes will look odd - you could look over in C&C if someone's made wintry versions of them.