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English: The Gen. Antonio Luna Parade Grounds, or commonly known as the Sunken Garden, is a 5-hectare natural depression found on the eastern side of the campus and at the end of the Academic Oval circle. Sunken Garden is enclosed by the U.P. Diliman Main Library (also houses the School of Library and Information Studies), College of Social Sciences and Philosophy's Department of Psychology, College of Education, Student Activity Center/Vinzons Hall, College of Business Administration, School of Economics and College of Law. The Grounds was originally a property of the UP Reserved Officers' Training Corps when the campus was founded in 1949.

Gen. Antonio Luna Parade Grounds acquired its name Sunken Garden due to its basin-shaped low-level formation that has the deepest point of 65 meters above sea level (contrary to university's height of over hundreds of meters above sea level).[34] The Sunken Garden is the venue of the annual U.P. Fair as well as for sports tournaments, including football, frisbee and volleyball. Sometimes, the Department of Military Science and Tactics hold training in the area.

According to local lore, the Sunken Garden sinks by about two inches every year. Though this has not been verified in any study, some have posited reasons for the sinking: one is that it is because of underground trenches over the campus' sewer system that connect to the Marikina Fault Line, an active geologic structure that runs across the east of Metro Manila.[35] Another theory is that the depression was due to the emptying of former streams in the Sunken Garden that were prominent in the 1950s. These streams formerly run from the Katipunan Avenue, going to the garden itself and leaves the campus for the Commonwealth Avenue.[1][2]