The pre-cast concrete Crown Buildings at Penrallt, said to be known by some people as “Alcatraz”, are set to be turned into “much needed” local homes. The Crown Building At Penrallt In Caernarfon. Cyngor Gwynedd purchased the former Crown Buildings in March 2024 as part of its Housing Action plan. It describes how the project would see the offices converted into a mix of one, two and three bedroomed units. The Crown Building itself divides opinion; locals often call it Alcatraz,” planning documents added.