Enough about me, onto the terrain...
Let's start with the park in the lower left hand corner of the above shot. Using green scrubber pads for hedges is an old grognard trick. To really make them look sharp, I've drybrushed them with green and yellow paint. To keep their shape, I drilled holes through the craft board and hot glued short lengths of dowel for posts. In the shot to the right you can see that I also folded them in half. This gives them more thickness and a nice round curve to the top, and it also makes them more stable and less crushable in the storage box.
The sidewalks are sort of modular. In this shot you can see how they almost line up. Sometimes you get weird artifacts where one block of sidewalk sits alone in a corner, but for the most part, they help tie each the individual tiles together into a unit.
The fountain was made from a 1.5" PVC cap glued into a plastic flower pot base. It needs blue paint and fake water yet, and I'm thinking about painting a miniature gray and sticking it on there as a statue. That might make it tough to store that tile, though, so I haven't decided.