I thought he took advice from his Generals?

Why not, then, from an Admiral? The top Admiral. The top flag officer in the whole United States armed forces? Via Think Progress...

“I’d like to see it shut down,” Adm. Mike Mullen said of the Guantanamo Bay detention facility. Asked why he thinks Guantanamo Bay should be closed, and the prisoners perhaps moved to U.S. soil, Mullen said, “More than anything else it’s been the image — how Gitmo has become around the world, in terms of representing the United States. … I believe that from the standpoint of how it reflects on us that it’s been pretty damaging.” Nevertheless, Mullen said he’s “not aware that there is any immediate consideration to closing Guantanamo Bay” inside the Bush administration.

When an Admiral (or General) says "pretty damaging" he means "to my mission," which translates to "gets my troops killed." Admirals and Generals care about stuff like that, even if the Bush gang doesn't.

Close it down.