The above map shows the border between the United Arab Emirates (yellow) and Oman (green). Inside the UAE is a tiny enclave of Omanese territory called Madha. It consists of about 29 square miles. Inside that enclave is another enclave of UAE territory called Nahwa, which is under a square mile in area. At the link, you can view pictures of this enclave within an enclave.
Link via Dan Lewis | Map: National Geographic Society