Guest Peninsula is a snow-covered peninsula about 45 miles (70 km) long between the Sulzberger Ice Shelf and Block Bay in the northwest part of Marie Byrd Land, Antarctica. Mitchell Peak, located on the peninsula, was sighted by the first Byrd Antarctic Expedition in 1929. This feature was defined and mapped as "Guest Island" by the United States Antarctic Service Expedition in 1940. It was determined to be a peninsula by U.S. Geological Survey cartographers from air photos taken by the U.S.