A tourist day with alternatura. The Blue Cave (Blue Grotto, or Modra špilja) on Biševo. Blue, because the sunlight bounces off the sandy sea floor and so passes through ~30m of water to get into the cave. Discovered by an Austrian painter or crawled in through a small gap in the cliff before returning the next year to blast a bigger opening. The green cave (Zelena špilja), which is green because blue was already taken.