The entrance to Golondrinas is a roughly circular opening 50 meters across, east to west, and 60 meters wide. The edge of the pit is surrounded by vegetation that hangs down into the void, except on the low side, where there is a clear bedrock strip about 10 meters wide. This limestone ledge slopes down slightly toward the pit and is deeply dissected by solution fissures. The walls of the pit are undercut on all sides, and they continue to bell out all the way to the bottom, giving the pit a shape resembling a megaphone. The longest drop possible is 376.4 meters, off of the high side. This may actually still be the longest freefall drop in any cave in the world.

Golondrinas is formed on a fault, which is visible on the northwest wall at the entrance. The fault is nearly vertical, with the beds on the eastern side having moved down relative to those on the west. The massive beds dip 20 degrees to the southwest. The entire southwest wall of the entrance pit may be formed along the fault plane.

Looking down the pit, the features of the floor can be dimly seen, including breakdown blocks and drainage patterns. As the descent is made, perspective on the true scale of the pit often does not occur until partway down. While descending, the moss-covered walls gradually recede, until the closest wall is about 60 meters away from the 333- meter-drop's landing point. Two prominent openings in the west wall can be seen, one at -175 meters below the high side, and the other at -250 meters. The lower one has been reached by climbing the wall from below. It is essentially a large alcove, with a steep slope of loose guano that leads up to the ceiling.

The pit floor is semi-circular in shape, 130 meters wide and 270 meters long, with the long axis oriented northwest. The floor itself has 75 meters of relief, expressed for the most part as wide gentle slopes that feed two stream valleys. Breakdown, talus, bird guano, and guano sediments cover the floor, with occasional flowstone masses in some areas. Although the room is lit by natural light, it is too dim to allow significant plant growth.

While there are many "bird pits" in the Tamapatz area, Golondrinas was among the first known and remains the best example. The large population of white-collared swifts makes it a significant wildlife habitat that deserves conscientious conservation. Dave Whitacre, Devi Ukrain, and other ornithologists, in association with the Chihuahuan Desert Research Institute, took a census of bird populations at Golondrinas and other pits in the area over a period of years. A count in February 1976 showed over 25,000 swifts living in Golondrinas, but since that time their number has apparently been decreasing.

The swifts roost in alcoves in the pit wall near the bottom. When the morning light filters down from the entrance, the birds begin their exit. A bright sunny day causes the largest flight, but the pit never completely empties of birds. The swifts, unable to fly straight up, ascend in a large spiral, which becomes tighter toward the top as the pit narrows. Finally they break over the edge, forming a continuous stream at the flight's peak, a river of birds that fades into the karst valley to the east in search of food. In the evening the birds return in waves, circling above the pit in a toroidal formation. At intervals a portion of the flock will suddenly dive into the pit in a spectacular freefall, pulling up before the bottom to attain their roosts. An unfortunate few misjudge and hit the lip or walls.

Meanwhile the green conure, which tends to live higher up in the pit walls, must make its way in and out without being speared by a plummeting swift. The conures, as with other parrots, usually fly in pairs and groupings of pairs. The bright green plumage of the bird provides a spectacular flash against the high side pit wall.

A variety of other life inhabits the pit. The first explorers reported being visited by an "animal the size of a cat" while spending the night on the bottom. This could have been a tayra, which has been reported from Hoya de las Guaguas, a similar pit. Several bats are known from the pit, Anoura geoffray and Artibeus jamaiscensis. Salamanders up to 25 centimeters in length are common on the pit floor, as well as a variety of invertebrates, the largest of these being the whip scorpion, or vinegaroon.