The Batagaika crater in eastern Siberia is the biggest permafrost crater in the world. According to research published in 2016, the crater wall has been growing by a yearly average of 20-30 meters per year over a ten-year observational period. The local Yukatian people report hearing ominous noises, leading some to call it a portal to the underworld. The depression is in the form of a one-kilometre-long and growing. The land began to sink due to the thawing permafrost in the 1960s after the surrounding forest was cleared. Flooding also contributed to the enlargement of the crater.
info source: wikipedia
NASA Earth Observatory images by Jesse Allen, using Landsat data from the U.S. Geological Survey., Public domain, via Wikimedia Commons