The Telescope is a furniture you can build (the Outdoors page).
In-game description
A brass telescope on a wooden tripod. At night, E to look through it: the nearest dungeon or lair you haven't found yet, within 150 tiles, is pinned on your map. Once a night.SHOWN IN THE BUILD RING
Building it
It costs 4 
Wood, 2 
Bronze Ingot, 1 
Glass, 1 Water 1 Earth 1 Wind spirits. It needs 1 Jewel first. Take it down with DISMANTLE to get its cost back (see Building).
