The Crystal Bridge can be unlocked with a Spirit Key to grant access to the 3rd Floating Island. In order to activate the bridge, a Spirit Key is required to open the Spirit Lock. This will use the player's key to form the Crystal Bridge. Currently, only the Crystal Guardian drops the Spirit Key. On the 3rd Floating Island is the Lonely God and Crystal Lodes, along with Petrified Bushes and Petrified Trees.
After summoning the bridge, the structure will disappear in 30-60 seconds.