At one side of
Geologically Improbable Mountain, two tunnels emerge. These aren't
really tunnels, just portals. The upper one is only 2" deep and the
lower one is about 12" deep although they both go about 10 feet
behind the mountain.
Real tunnels are maintenance problem. Animals
like to live in them. Track maintenance is complicated by the
inaccessibility of the track inside. Train wrecks inside are hard
to remove. A common solution is to create access ports above longer
tunnels. My solution was to "daylight" the region behind the portals to allow easy and level access
from the other side. This method allows one to actually walk into the
"tunnel" so that maintenance of the track is no more difficult than
any other track.