Figuratively speaking it is common to call a teams stadium a "fortress" during an unbeaten run at home. FC Duruji Kvareli however took the saying literally.
The Kvareli Fortress, located in the small town of Kvareli in Georgia, was constructed between the 17th and 19th century, renovated in 1985, and became a soccer stadium for the local team. Duruji Kvareli turned the fortress into a pitch with a capacity of about 1,000 fans where they hosted their home games, making it perhaps the most unique stadium in the planet.
Durji Kvareli featured in the Georgian first division between 1994 and 1996 but by 2017 plummeted to the 5th and last division before folding. Even though the town's professional team doesn't exist anymore the local amateurs clubs still utilize the fortress/stadium and always have it's doors open to visitors.