The best months are April–May and September–October, when daytime temperatures stay around 20–25°C and the light is good for photographs. Summer (June to August) is hot, with afternoons over 35°C and large coach groups arriving daily from the coastal resorts.
Winter is quieter and the travertines are even more striking under a low sun, but the inland plateau gets cold — December and January nights drop below zero — and the thermal water is then a serious attraction in its own right. The site is open year-round. Sunrise (the gates open at dawn in summer) and the last two hours before sunset are the best times to walk the travertines: the light is gentler, the heat manageable, and the day-trip crowds gone.