After spending a night in Sparta I was really pleased to visit Mystras only about 20 minutes away by car.
Mystras is among the best preserved Byzantine fortress cities and really quite enchanting. The fact its Byzantine means it was heavily influenced/funded by the Byzantine Greek Orthodox Church of Constantinople so within there are several churches with old icons and frescoes including a garden-like small convent.
There are 2 entrances: one at the top and one at the bottom. I drove to the top and walked down 1/2 way, returned, got the car and used my same ticket to enter at the bottom... a guard told me this legal trick. Its a trek otherwise. If you are in the Sparta area you have to visit Mystras!
Mystras - is a unique example of a Byzantine fortified town, with its walls still intact. Its setting is quite exceptional, overlooking the Evrotas Valley and Sparta from a steep spur of Mt. Tayetos, and its Byzantine churches, monasteries, ruined palaces and houses, testify to its former glory as ancient capital of Morea (the old name for the Peloponnese).
It is a truly amazing experience to ascend the lush green hillside and wander through the narrow winding streets of this medieval town which once had a population of up to 42,000 (though more typically, 20,000-still an impressive number) with some of the finest examples of 14th-15th century Byzantine architecture in Greece, and superb frescoes in its many churches.