Saturn's moon Titan is bigger than Mercury, and so far as we know, it's the only body in the solar system besides Earth that has surface liquid. Near Titan's north pole, there's an entire system of lakes filled with liquid methane. These lakes show tributaries that hint of a weather system in which methane evaporates and then rains over the land. We know this because the Cassini probe scanned Titan with radar, which bounces off land but is absorbed by liquid. The rate of absorption indicates depth.
Kraken Mare (literally, Kraken Sea) is a huge lake near the north pole of Titan. Cassini pinged it with radar many times. On one such pass, the track of the radar went over land, then the main part of Kraken Mare, and then a bay called Moray Sinus (no, not the nose of the eel; sinus means bay, and the name comes from the Scottish firth). As the radar pulses pass through the liquid they get attenuated, fainter, before reflecting back up to Cassini. By measuring the attenuation the depth can be measured.
The scientists found that Moray Sinus has a depth of about 85 meters, which is impressive. But over the main body of Kraken Mare they got no reflected pulse at all. Local conditions can make it hard to know exactly how much radar is absorbed by the liquid (for example, if the surface is rough with waves, which is actually likely) but the lower limit for their measurements is 100 meters. If conditions were actually good, then it means the depth is at least 300 meters.
For reference, the average depth of Lake Superior is around 150 meters. While impressed by the otherworldliness of a moon with liquid methane lakes, I am also intrigued by the naming of such lakes, and wish I could've been a fly on the wall when those were proposed. Read more about Kraken Mare and the other lakes of Titan at Bad Astronomy.
