Gwanaksan, the mountain stretching across parts of southern Seoul and Gyeonggi Province, always welcomes hikers of all ages with a total of 15 hiking trails that can be approached from multiple subway stations in Seoul, Anyang and Gwacheon.

With its subway-accessible trails, Gwanaksan is one of Seoul's most popular mountains, especially among those in southern Seoul, in any season.

This summer, an outdoor swimming pool opened on July 7 in Gwanaksan, but the seemingly endless monsoon rains, heat wave and landslide risks had many people staying away from the mountain for a few weeks.

The mountain began receiving its usual number of visitors only just recently after the rain-soaked month of July.

Visitors can spot the narrow entrance to Sillim “gyegok,” which refers to a valley created by a stream, after a 10- to 15-minute walk from Gwanaksan Station Exit No. 1 on the new Sillim Subway Line.

With the cold, fresh water flowing with decent force, the gyegok has become an oasis for children to cool off and play with their friends and family.

The water in this natural swimming hole is not deep enough for adults. But that does not mean Sillim Gyegok is a boring place for grown-ups.

Tunnels created by trees provide sufficient shade for all visitors to cool off and relax, shielded from the scorching sun.

Last Saturday, many people were spotted sitting on folding camping chairs, dipping their feet in the cool water. Some chose to lie down on picnic mats and enjoy the latest Netflix series outdoors.

“I do my high-speed running on Gwanaksan’s walking trail. And I heard that an outdoor swimming spot would be opening this summer. I went to Caribbean Bay with my family several years ago and felt that the place was too crowded,” a 39-year-old housewife surnamed Kim told The Korea Herald on Saturday.

“We decided to avoid extremely packed tourist destinations this summer and hoped to make a great memory at the nearby gyegok at Gwanaksan. I think we made the right choice,” the mother of two boys said.

Lee shared her satisfaction with Gwanaksan’s natural swimming spot -- its easy accessibility, lifeguards on duty, clean changing room and less heavy crowds.

“Sillim gyegok might not have the fancy rides and thrilling artificial waves you find at water parks, but I believe it has everything to be a tucked-away summer vacation spot where you can have memorable experience with your friends or family members,” Kim added.

Another hiker who wished to remain anonymous said that he was more than happy to take a short break after coming down from Yeonjudae -- Gwanaksan’s peak.

“Those on vacation seem to be having a lot of fun downstream. But the water is also an oasis for exhausted hikers. Splashing one's face with the cold water and dipping one’s feet in can relieve all your stress at once,” the hiker said.

Meanwhile, an overnight program at the mountain is also available.

The Gwanaksan Gyegok Camping Forest offers hands-on activities, including decorating one's camping tent, observing water creatures, looking for Gwanaksan's night insects, stargazing, rope games and walking the mountain’s trails, for families with children as well.

Families with children aged 6 to 11 can apply to participate in the program via the official Reservation for Public Service website.

Participants do not need to worry about camping equipment as the program offers both four-person and five-person tents and picnic mats for 10,000 won ($7.49).

Groups with a maximum of five people can participate in the camping program, with children accompanied by a parent.

The overnight program starts at 3 p.m. on Fridays and Saturdays.

The Gwanaksan Sillim Gyegok swimming hole and the Gwanaksan Gyegok Camping Forest are open for operation through Aug. 27.

More inquiries can be made at the Gwanak-gu Office.