On a budget, weigh it — Day Trip to Pompeii isn't cheap for what it is.
€90–180 pp (tour) / ~€40 DIY
An astonishing, walkable ancient city — frescoed houses, a forum, plaster casts of victims — that rewards the effort. But it's a serious commitment from Rome: a fast train to Naples then a local line, easily 10–12 hours round trip, and Pompeii itself is vast, hot, and largely unshaded.