The Excalibur Lighthouse was originally the home of Captain Britain and his girlfriend Meggan. Once the team Excalibur was formed, the other members moved in, each living on different levels. At times the limited space would be found to be annoying to any involved, which occasionally led to fights. The lighthouse also included a gym for Nightcrawler to exercise and keep in shape, and other facilities for the team.
During Inferno, Rachel Summers had a nightmare and stormed out the lighthouse straight through the roof, leaving a massive hole which was eventually repaired. The lighthouse is also where the team retreated after the events of the Cross-Time Caper, and where they shortly after met Galactus.
After a bomb attack from the Gratecrasher's Technet, its upper portion exploded, and once Excalibur hosted the orphaned Technet from previous leader, the alien team started a reconstruction job that gave to the lighthouse a more fungus-modern appearance. During these renovation works, the Technet added a comm-room to the original lighthouse, and in Excalibur #49, when Nightcrawler tries to locate Necrom, it's shown the possible location of the lighthouse as being on the coast between Liverpool and Southport, on the west coasts of England.
It was definitely destroyed by Meggan, in an effort to remove Merlyn's manipulation over the team. Since the Lighthouse was the fulcrum and the door connecting the different multiverse realities, and in each one existed the same lighthouse; with the destruction of the "glue" who kept all the worlds together, the alignment of the realities was destroyed and therefore the cross between the worlds made impossible, and the energy matrix that kept everything together dissipated.