During your stay in Rethymno, which is about in the centre of the island, and should you have just enough time, you could tour around and visit many beautiful places.
At a short distance, you could visit the ruins of Ancient Eleftherna and the post-Minoan cemetery of Armeni, or the historic monasteries of Arkadi and of Preveli.
You could also go to the lovely southern or northern beaches; or maybe, walk across the gorge of Prassa and of Patsos.
You can visit Chania, Samaria gorge, Elafonisi, Kisamos on the west side of the island and
Heraklio, Knosos, Festos, Matala, Ag. Galini, Ag. Nikolaos, Sitia on the east side of the island.
For the your transportation you can use the local bus or rent a car.