There's many beaches on Gotland, in fact many people from the main land (Sweden) take their vacation on Gotland just because of the beaches and the possibility to take a bath almost wherever they are on Gotland.
The best tips a can get you is to go to the east side of Gotland, choose Ljugarn or Herta, that's nice beaches.
However, if you like to take a bath together wit a lot of people, then you should go to Tofta on the west side or Sudersand in the north part of Gotland.
The beaches that we show pictures in and give a little information about is not all of the beaches of Gotland. There's at least fity good beaches, allmost whereever one goes there's a beach close by.
Bring your swimsuit!