9-11 Museum being built, but should it be underground?

The Philadelphia Bulletin writes about the construction of the 9-11 museum, which is taking place 70 feet below ground.

While this is a very good article for reading, it did make me wonder - should this really be below ground, if I'm reading this correctly? I assume there will be a special structure that'll be located above ground from where you enter, but even so, this is a very challenging question about if this should really be underground.