Feng Shui: The Lost Island
A Secret Lair is the group’s refuge from the world. No one knows its location, and that is its number one defense. The more schticks the group has in Secret Lair, the harder the lair is to find. One schtick amounts to a series of secret rooms beneath the garage; two schticks provides a completely hidden or disguised facility, perhaps in an abandoned warehouse or hangar; three schticks gets the group a remote arctic base, elaborate subterranean cave system, or obscure tropical island. Each schtick also grants a +1 AV bonus to Intrusion checks made to secure the Secret Lair. Secret Lair and Headquarters can be combined into a single location by getting schticks in both. If the Secret Lair is large enough, you can even park The Van there.
AllSecret Lairs have one thing in common: GMCs cannot know about the place unless a PC shares the secret with an outsider. The GM may not have GMCs show up there unless the PCs open themselves up to the risk. The GM gets to decide what GMCs do with the knowledge they have (looking in your direction, Alfred).