Monastir and Mahdia work best as a combined Tunisia Sahel destination rather than two separate dive trips. Monastir gives you the airport, marina, Kuriat Islands access, and easy rail links. Mahdia adds the stronger pure dive product, especially if you want a quieter base, sandy beaches, first dives, shallow wrecks, and a step-up path toward deeper wreck diving. This is not a high-voltage pelagic destination. It is a practical Mediterranean option for summer and early autumn when water warms to around 24°C to 27°C, winds ease, and snorkeling, training dives, and relaxed boat days become straightforward. The standouts are Kuriat for turtle-linked conservation context and clear-water island outings, plus Mahdia's wreck portfolio led by the shallow Napoli and deeper PLM 20.