The Magic Roundabout at Hemel might seem complicated but you just have to break it down into its components. It's 6 mini-islands joined by 6 very short roads that happen to be in a big circle. It works really well!

The words roundabout and island are more-or-less interchangeable, BTW. A mini-island is one with no middle to go round, or just a painted circle or a raised lump. It's acceptable to drive straight over it. I call it a 'logical island'.

More common than the Magic Roundabout (are there others?) is the double island, two logical islands with co-incident edges. Sometimes three. These need caution! Again, break it into parts: it's just two island with a zero-length road between. I call them 'occluded islands'

Aylesbury had a nice collection of doubles and triples but has recently taken to reinstalling traffic lights which is a backwards step IMO. (I was driving in the US recently; God! All those traffic lights!)