One of the best things about living in Paris is that we have the time to explore the not-so-obvious aspects of the city. The Eiffel Tower is hard to miss, but there are many places that are hidden, or not easily seen unless you know where to look. In my latest post on Gridskipper I run down some of the best underground sights in Paris–that is, literally under the ground.
Update: Underground Sightseeing in Paris made the list of Best Maps of the Week on Gridskipper.