Pylons form a fast-travel network — place a biome's pylon near enough happy town NPCs, then tap any pylon on the map to teleport between them. Each biome has its own, plus the Universal Pylon from the Zoologist.
Buy a biome's pylon from a town NPC who is happy living there (you need at least two NPCs nearby), place it, then tap it on the fullscreen map to teleport between any placed pylons.
Each pylon is sold by a town NPC living happily in the matching biome. The Universal Pylon works anywhere and is sold by the Zoologist once your Bestiary is nearly complete.