I have no idea what this building is

Photographer: Doug L.
From: Day Five (Across the Irish Sea to Wales)

I have no idea what this building is

Our walk on this very hot day took us out on a wooden pier extending into the harbor. A nice breeze gave us some relief from the hear, but a nice big bottle of Fanta worked even better. I searched the internet trying to figure out what this building is, but to no avail. My guess is that it is/was some sort of royal/government structure.