There Were A Number Of Signs

Runway

A runway with the number 26 in white on it.

Sea base

A reinforced-looking entrance to some kind of undersea bunker labeled with the number 23.

Fin

A red stabilising fin with the number 512 sticking out of snow. It may look familiar to some.

Hideout

A village house turned some form of not all that well-hidden hideout, with a poster on the wall, and another on the floor pretending to be a small carpet

Tunnel B2

A service tunnel with a door labeled "B2". You probably shouldn't go in there