In the US, there's a good chance you haven't even left your state either
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If I drive for 4 hours, I'd end up in the ocean.
We don't have that problem in the UK. Roundabouts.
We don't have that problem in Sweden either. Not only do we have roundabouts, but we also have roads with turns in them.
You've made me wonder if it would be legal to spend 4 hours in a roundabout without taking an exit.
So there is not law or rule specifically about having to exit a roundabout. So in theory, yes you could. But you are likely to have the cops come ask you to leave before that, as that could possibly be seen as dangerous driving.