The lighthouse is a rather tall building, and

The Lighthouse

can be found nearby the Northern Tower Town by following the twisty dirt road. It appears that nothing spawns on top of the tower, however, basic loot can be found at the foot of the lighthouse and as well as the small toolshack that is right next to it.

it is compairable to the size of Giant Zombies.

Lighthouse view

It's a great view on top of the Lighthouse. You can see the Northern Tower Town from here.