Aogashima Island, Japan - 青ヶ島 日本 while located in the Philippine Sea, is a volcanic Japanese island. The name Aogashima literally means 'blue island' and is technically part of Tokyo despite being located over 200 miles from central Tokyo.
Melissani Cave, on Kefalonia Island in Greece, features a sky-blue lake within the cave. The lake is shallow and clear, and is covered with stones at the bottom. The cave was rediscovered in (In Greek mythology, Melissani was the cave of the nymphs.
Bled Island in Slovenia . a town and a municipality in Slovenia, and like most European towns, a popular tourist destination for its scenic beauty. The town is particularly popular for the glacial Lake Bled.