If they particularly enjoyed spending time at the beaches, cliff jumping etc. I’d have a look at:
Sardinia - amazing snorkelling, fantastic beaches, beautiful nature, great food. Areas to look at: Villasimius, Costa Rei, Pula, Stintino, Costa Paradiso, Orosei.
Sicily - great food, gorgeous beaches, amazing diving/snorkelling. Areas to look at: San Vito Lo Copo, Fontane Bianche, Giardini Naxos, Cefalu.
Malta - brilliant snorkelling, great coasteering, gorgeous coves/caves. Areas to look: Gozo, Mellieha, Bugibba/St Paul’s/Qawra.
Corsica - fabulous beaches, great snorkelling, gorgeous landscapes, great little restaurants and bars. Areas to look: Porto Vecchio, Propriano, Bonifacio & Bonifacio Coast, Cap Corse, Saint Florent.
Ibiza - good beaches, great food, shorter flight time. Areas to look: Cala Tarida, Santa Eulalia, Cala Llonga, Es Caná.