One of the earliest terrain items I've created, after dungeon walls and some woods and rocks is winter terrain. Having often seen use, this terrain can be used in almost any genre and world; Marines invading arctic base of an evil mastermind, friends of Drizzt adventuring in Icewind Dale, An icy planet to be explored...
When looking at how much atmosphere these terrain items create and how easy they are to create, I'd say anyone creating gaming terrains should create a set of these! My old D&D miniatures map actually works quite nicely with these, it's always been a bit too light for a dungeon floor (for saving in ink costs???). I hope to get a good set of base ground terrains some day, one snowy, another forest base that can be used as plains etc... But for now I'm mostly using maps.
How were these pieces done?
Cardboard base, this time a bit thicker than 1mm. I don't recall fully how I did all the bases after that, but I got a bit too much distortion - currently I've started to glue pieces of styrofoam before applying filler paste. I've used while pigment with the paste, but I've now realized that I can't find the good old Polyfilla filler powder anywhere, so I need to find something as well (or better!) suitable for modelling purposes.
Anyway, trees are plain wire trees with a layer of greyish brown-dyed filler, and I've applied a few layers very thick filler on the branches. Spruces are created from cutting bristles from a brush, putting them on a wire, placing another wire on it and then twisting with a drill. The spruces are dyed dark green with brownish shade. And then again, thick white filler is applied.
Same method goes with other components: Rocks are just rocks, and filler on them. And I've used bristles to create hay sticking from the snow too.
Campfires are made with my fire technique. The two buildings with snowy roof have detachable roofs - I've created one normal one for each and one snowy one. Rocks have a detachable snow cover I've created by pressing tin foil on the rocks, then applying pieces of newspaper soaked in water-wood glue mixture on it and after several layers have dried, I've cut off the excess and applied white filler.
I've added some white paint to the snow and finally, I've chosen one side from each piece I've brushed some grey-blue paint.
Here's one diorama picture where I've used these models: Diorama: Winter fight