There are 11 Stag Stations in the game. These stations are the part of the Stagway fast travel system and allow you to quickly move around the world. After finding the 10 findable stations, the 11th becomes accessible.
Most stations require paying geo at a toll machine to unlock but some only require flipping a switch. Once activated, you can ring a bell to summon the Last Stag who can bring you to any other active Stag Station.
Stag Stations can be found in the following areas:
Queen's Station (in Fungal Wastes)
City Storerooms (in City of Tears)
King's Station (in City of Tears)
Distant Village (in Deepnest)
Palace Grounds (in Ancient Basin, referred to as "Hidden Station")
You can use this fully interactive map
to see the exact location of each station. Uncheck everything except "bench and transport" in the control panel.
Once you unlock 5 Stag Stations, this achievement will unlock.