Pompeii has been described so many times that I don´t need to add that much. But if you have never been there, go there or you will miss the most amazing archaeological site anywhere. History really does come alive here, despite the huge crowds. Unfortunately I could only be there for a couple of hours, but I certainly hope to return there as soon as possible, hopefully also to visit Herculaneum, which supposedly has the more interesting remains (if that´s at all possible), and maybe the Villa Oplontis. If you can, combine a visit to Pompeii with a hike up Mount Vesuvius (auto road, walking route for the last few hundred meters over slippery terrain) so it all comes into perspective. The mountain is very interesting both from a historical and from a geological/volcanological perspective and offers great views of the Bay of Naples (unless it´s foggy or the smoke from the crater covers your vision), one of the most beautiful vistas in Europe.