This is Kelimutu on the island of Flores in Indonesia. These unusual crater lakes are the result of volcanic activity. There are actually three lakes and each contains different colored water.
"Tiwu Ata Mbupu (Lake of Old People) is usually blue and is the westernmost of the three lakes. The other two lakes, Tiwu Nuwa Muri Koo Fai (Lake of Young Men and Maidens) and Tiwu Ata Polo (Bewitched or Enchanted Lake) are separated by a shared crater wall and are typically green or red respectively. The lake colors vary on a periodic basis."
Apparently the color changes are due to chemical reactions from the minerals in the volcano. These lakes are a popular tourist destination in Indonesia. I think I need to create a bucket list and on it I am going to add a visit to at least one volcano somewhere in the world.
The stamp is a "Greeting Stamp" with a lovely floral centerpiece and candles.
Postcrossing card #97