Sure, there are quite a lot of islands in Greece. There are obviously a lot of non-volcanic islands, there are also a lot of volcanic islands. But there is also..a tiny island which is literally a volcano itself. All of it. And it's called Nisyros! It's an island in the Dodecanese, south of Kos and next to Tilos.
Nisyros has got 5 craters in total, but the big one - called Stefanos - definitely stands out in the middle of the island. It can be seen from all around the island, especially if you get high up. The views are obviously breathtaking and just seeing the crater from afar makes you want to get there and explore it.

And guess what, this is possible! You can drive to the crater, pay a 3 euros entrance fee and walk right into the crater. Be careful not to walk barefoot, as the ground is scorching hot at some points. Also, don't go near the smoking holes left and right as there could be toxic sulfuric fumes coming from beneath the ground.