Lighthouse can either mean an Adventure Map location or Castle specific building of the same name. They both have the same effect, increasing movement points by +500 when heroes move on water tile with a boat. The bonus is cumulative meaning that owning two Lighthouse increases all heroes' movement points by +1000 on water. The bonus is calculated after a possible bonus from Navigation skill. In other words, Navigation only affects the base movement on water.
Lighthouse as Castle specific structure
Lighthouse can only be build in cities with access to water, meaning that adjacent to the garrison tile must be at least one tile of water.
Prerequisite: Shipyard Cost: 2000 + 20