Impressive work Darren. One of the great things about rigid foam is its light weight. I made this corner mountain with foam modules so it can be taken apart if I need access to the track inside the tunnels.
A hot wire doesn’t make enough mess for me. I used a keyhole saw or steak knife for the cuts and a wood rasp/60 grit sandpaper for shaping. I used mold-a-scene/sculptamold for final shaping.