It's just the Maremmani's luck that the view is as good underwater as it is above it! Then again what did you expect from a region that dips its feet into the Tyrrhenian Sea, or as they call it, the Mar Tirreno?
Seasoned divers can enjoy dive sites that extend to all sorts of depths. There's even a few sunken ships below the shores of Giannutri and Giglio Island!
The waters around Giannutri Island, in particular, have this amazing clarity because motorised vehicles are banned from the area. The only way in is in scuba gear, so you can just imagine how beautiful the undisturbed sea environment is.
If you know your way around dive gear then you really don't need a guide. Just rent any necessary equipment from Porto Santo Stefano and hop on the next ferry to Giannutri Island.
Make sure you're early though, the island only accepts a set number of tourists a day, so you might want to book ahead.
For newbies to the diving world, it's probably a good idea to book a few lessons. There are plenty of dive schools in Porto Santo Stefano.
Otherwise you can always rent a scuba mask and just stick your head underwater. The reef is still spectacular!
Photo: Riandreu via Flickr.