Konstantinos’ place has the perfect location in Karvostasis - it is in a quiet street right next to the beach. The bus stop is a minute by foot. The property is well maintained and Konstantinos is a very pleasant host. You get picked up from (and delivered back to) the port which is always a nice touch. Sheets and towels are changed on more than a regular basis, so I give his place an OCD-approved seal! :) All in all, this is the accommodation to go in Karavostasis.
The bus that stops nearby takes you to Chora and you can take another bus to the Agali beach from there. I would recommend getting a car for a few days to visit the beaches more easily. A few peaceful beaches are accessible by foot as well and you have a boat that takes you to the Katergo beach from Karavostasis (though going down/up the cliff by foot is more fun).