Laser-cut masonite hardwood.

You get the following ittems:

2 double track tunnel portals and 4 wing walls.

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

Measurements are:

Portals - 4.5"L x 3.25"H x 1/8" thick

Wing walls - 4" L x 3.25" H x 1/8" thick

Double stack trains will fit through the opening.