The Kostas and Mary hotel in Skiathos is a great choice! From what I hear, the hotel is conveniently located close to town. The uphill climb may depend on your starting point, but the area is generally known for its charming hilly streets. Contacting the hotel directly or checking online reviews for more specific information would be a good idea. I have planned my vacation at Si Como No Resort Spa & Wildlife Refuge this year, and I can't wait for this trip because learning something new is always an incredible experience. I hope you and your friends have a fantastic vacation, and good luck.