Pētera ala is a geological and geomorphological natural monument on the slope of the Vējupīte ravine of the Gauja tributary, in Sigulda. It is located in the territory of the Gauja National Park.

Peter's cave is a narrow crack in the red sandstone wall. Its height reaches 6.4 meters, length 6.3 meters (under the sandstone ceiling only 4 meters) and width 2.3 meters. The cave is notable for its great cultural and historical value.

Peter's Cave is considered an ancient place of worship. In 1997, historian Andris Grīnbergs discovered petroglyphs high up in the cave walls. In total, at least 42 different petroglyphs have been preserved in the cave. Also, individual engravings with year numbers have been found in the cave and rock walls since the 18th century.

Since the end of the 19th century, Peter's cave has been often described in various literary sources.