Linow Lake is really a water-filled volcanic crater. It's a very pretty little lake, but with some interesting features. Several small vents line the wall of the crater, spewing hot gases and water. Bubbles in the lake indicate there are more vents below the water line. The changing mixture of chemicals in the gases cases the lake to change colors from time to time, from red to deep green to even blue.
Lake Linow - the "changing color lake"
There's a rather nice little coffee shop on the short of the lake, making this a good place to stop for an afternoon drink when touring the highlands. If you explore one of the vent areas near the café, do take care of your footing. In places the ground looks quite solid, almost like old concrete, but is really very soft and in some cases is underpinned by the running water.
Admission to the park area of Lake Linow is 25,000 Rupiah (1.50 USD). A stop at the lake is included on most highlands tours, such as those offered by Manado-based Safari Tours.