Trevlac Tunnel for my model railway 00 gauge layout.
This is a two minute video of how I made it in one day. It cost around £20 (2013). It is 4ft wide which is my (non-permanent) layout’s width. Then about 2ft deep and 9 inches high. I sprayed it grey and black and was going to cover it in gravel and grass but liked it as it was, so left it. If you use the insulating foam wear gloves and don’t touch it, as it is hard to get off.
UPDATE: I’ve since found an easier way using insulation foam board. Look at my video called ‘Calverton Layout 4 Pt 3’ and scroll to one minute in. https://www.youtube.com/watch?v=2nD4ur_59x8
Music is Mondo a go-go by Eat Static.
Internet search ‘Calvertfilm’.