The mountain has two tracks going through it. I followed Eric Siegel's instructions for the tunnels and hard shell.
The main tunnel is the Hoosac Tunnel.
http://www.boudillion.com/hoosac/hoosac.htm
The main portal is made from pink foam and balsa wood. I used basswood to carve the letters and numbers.
Now that the weather is changing, this will slow down.
Steve