In Duisburg, Germany there is a roller coaster you can actually walk on. It’s called Tiger & Turtle- Magic Mountain.
As you look closer you can see there is a portion that seems to go upside down.
You can view a guy’s walkthrough of it here
in other words this is a huge disgrace to roller coasters, im fairly certain you cant even walk on the portion that goes upside down, its essentially just some stairs.