Rather than going out and buying a mountain with a tunnel for your model railway, make your own customized mountain. A homemade mountain with a tunnel will save you money and will perfectly fit the theme of your railroad -- such as winter scene, autumn harvest or desert landscape.
Determine how big the inside of the tunnel needs to be for your trains to run through it smoothly.
Sketch a plan for the mountain, including measurements from Step 1 and the location on the track where the mountain will go.
Bend chicken wire into the shape of the interior of the tunnel. Cover it with plastic wrap.
Rip newspapers into approximately 1-inch-wide strips.
Soak the paper strips in a watered-down plaster slurry.
Cover the chicken-wire form completely with the plaster-soaked paper strips.
Mold modeling plaster over the form, shaping it into a mountain. Allow it to dry completely.
Paint the mountain to match your railway's theme. Add grass, trees, rocks, pebbles, dirt, fake snow or even small plastic animals.
Paint the interior of the tunnel black or dark brown.
Cover the entire finished product with acrylic finish for protection.