We had a really good semester in Karmi apartments. It was walking distance to the Centrum, we went there in 30 minutes. We also tried walking with 15kg backpacks - that took 1 hour, but went ok.
The apartment was big and comfortable. We had no problems while we were there. We recommend hiring some kind of vehicle to move around the island. There are lots of lovely beaches within walking distance from the main road.
Overall a lovely experience, will recommend strongly :)