There is a well surfaced 400 metre long causeway to the island, which is probably only covered for a short while at high tide.
When we visited on a sunny Tuesday afternoon in July 2016 there was some very loud music playing (we could hear it as we came down the Zig Zag Path on Alderney) but no sign of any party in progress.
Fort Clonque from the Zig Zag Path
Alderney from Fort Clonque
Looking north towards Burhou from Fort Clonque
Fort Clonque causeway looking north east up the coast of Alderney
Main entrance to Fort Clonque
Causeway to Fort Clonque