From Dragon Mania Legends (DML) Wiki
See Social System for information about friend-related features
The Lighthouse is an immovable building used to view information about the Recruitment Code. Selecting the Lighthouse will bring up the respective window directly.
The building is located on the smaller island branching off of the Main Island placed next to the Clan Fortress and Totem of Friendship. It does not need to be assembled or bought and is unlocked at Level 3 after beating Quest 2 (Mountain Trail).