1. The Basilica Cistern, also known as Yerebatan Sarayi in Turkish, is an underground cistern that was built in the 6th century during the Byzantine era. It is located in the Sultanahmet area of Istanbul, Turkey. The cistern covers an area of 9,800 square meters and can hold up to 80,000 cubic meters of water.

Some interesting facts about the Basilica Cistern include:

- The cistern was initially constructed to provide clean drinking water to the residents of the city during times of drought or siege.

- The columns in the cistern are all recycled, and are thought to have been taken from earlier structures.

- The cistern was forgotten for centuries and was rediscovered by a French scholar in the 16th century.

- The cistern features two Medusa heads that are used as column bases. It is believed that they were brought here from an ancient pagan temple.

2. The Basilica Cistern is open to visitors every day of the week from 9:00 am to 5:30 pm. There is also a sound and light show in the evenings, which takes place from 6:00 pm to 9:00 pm. The phone number for the cistern is +90 212 522 1259.

3. Tickets for the Basilica Cistern can be purchased on site. The price of admission is 30 TL for adults and 15 TL for students. Children ages 7 and under can enter for free. The cistern is located near several major tourist attractions, and can be easily accessed by public transportation.