Most impressive secret base/hideout
In the EU sometimes you need a covert base of operations for your dastardly deeds, rebellion, or for some personal purpose. What organization/individual/government in your opinion had the most impressive base, or an area of operations that you thought was different?
Echo Base imo, only reason it was found was because Vader knew the Rebels were there. The Imps just figured it was some pirate or smuggler base. Yavin IV too, but then it is the Rebellion, so they kinda had to master the whole staying hidden thing.
But I think Echo Base is my fav of hidden bases, just because of its location and structural layout.