Marshall doesn't currently allow visitors.

However, there's one in Huntsville, at the US Space and Rocket Center (also home to space camp, for those of us who grew up with that). On it's side, on the ground, in pieces/stages. When I was last there it was out in the open. Apparently it's now enclosed in it's own building after restoration.

There's a replica standing up in their rocket garden / rocket park; it is just a mock-up, not the real thing, wiki says it was done in 1999.

There's also a real one in Houston (Johnson Space Center), and of course the one at KSC.

Yep, the US Space and Rocket Center is a museum right outside the base. The Davidson Center for Space Exploration (seen here https://www.rocketcenter.com/admission) has a Saturn V rocket broken down into stages. I had an hour to run through there while on a work trip, wish I could have spent more time.