Carmona sits on a ridge above the Corbones plain, 33km east of Seville, and it is one of the most rewarding day trips — or overnight stops — in Andalucía. The old town is compact and unhurried, ringed by sections of Roman and Moorish walls, and largely untouched by the tourist machinery that runs at full speed along the coast.
The most remarkable thing here is underground. The Roman necropolis on the western edge of town is one of the largest and best-preserved in the Roman world outside of Italy — a sprawling city of the dead cut directly into the rock, with painted chamber tombs, carved stone sarcophagi, and an amphitheatre used for cremation ceremonies. It is genuinely extraordinary, and most visitors walk past it without much idea of what they're seeing. Give it time.
Above ground, the old quarter rewards wandering. The Puerta de Sevilla, the main gate into the old city, is an imposing double-arched Roman gateway that later served as an Almohad fortress. The Alcázar at the top of the hill is now a Parador — even if you're not staying, the bar terrace has views across the plain that justify the visit.
Carmona is cheaper and quieter than Seville, and frequent buses (the 228 line from Prado de San Sebastián) make the journey in under an hour. An easy overnight if you want to explore at a slower pace.