I actually didn’t even realize that there was a second city that was wiped out by the Vesuvius eruption that you could visit — Herculaneum, which is decidedly smaller than Pompeii, but definitely worth a visit.
It’s actually better preserved than that city, so it’s intriguing to explore; you get a slightly better sense of what the city was like pre-volcano-apocalypse.
Bonus: it’s about a billion times less crowded than Pompeii.
Also, if you want to see the grimmest thing imaginable, there are several little caves that have the preserved remains of some of the people who tried (and failed, obviously) to protect themselves from the volcano’s wrath.
