Laser-cut masonite hardwood.

You get the following ittems:

2 single track tunnel portals and 4 wing walls.

This is a kit, all you need is wood or white glue to assemble.

Measurements are:

Portals - 3.5"L x 2.75"H x 1/8" thick

Wing walls - 3.5" L x 2.75" H x 1/8" thick

Double stack trains will fit through the opening.