Drinking in the champagne air as we pass out of the shadow of the pines and into the sunlight that drenches the bald granite summit of Mount Bugak, the colossal city sprawls at our feet.
It's easy for Seoulites to forget - and for visitors never to realise - that just a few minutes' drive above the bustle of the megalopolis' central business district lie spectacular alpine roads, dramatic terraced parks, shaded mountain hiking trails and cool, deer-inhabit-ed forests.
At 342 metres high, Mount Bugak forms the back-drop to central Seoul. In 1392, Yi Taejo, the founder of Korea's last royal dynasty, the Joseon, built his palace, Gyeongbok, in the shadow of its southern slopes. With the mountain guarding the palace's rear, or north, and the broad Han river glittering to its front, or south, Gyeongbok's location offered superb fung shui. The city subsequently grew around the palace - so if there had been no Mount Bugak, there probably would have been no Seoul.
The Japanese, who colonised Korea from 1910 to 1945, built their governor's residence behind Gyeongbok Palace, taking advantage of the location's prestige and abundant qi. After independence - and also by no accident - the South Korean presidential mansion, the Blue House, was built on the site of the governor general's residence.
Mount Bugak has always, therefore, been a strategic feature and medieval city walls snake over its ridges. A more contemporary threat, though, demands more contemporary defences. With North Korea just 50 kilometres north of the Blue House, the walls and the mountain road that winds around Bugak's slopes are dotted with bases manned by South Korean soldiers.
Paranoia? Hardly. On January 21, 1968, 31 North Korean commandos, tasked with assassinating then-president of South Korea Park Chung-hee (the late father of current president Park Geun-hye) infiltrated this mountain. They made it to within a kilometre of the Blue House before being wiped out in a series of firefights.
Only in 2006 was the trail that climbs up over the summit of Mount Bugak reopened to the public. However, ID and registration are required before visitors - whose numbers are restricted - are allowed through the security gate.
The bloody drama of 1968 is one of the major draws of the trail. Post Magazine has been invited to walk it in the company of a platoon of United States troops - just a handful of the 28,500 GIs stationed in South Korea - whose stroll is part of their education about the country they are helping to protect. The soldiers are affable but they are not authorised to talk to the media.
CHANGUIMUN, A MEDIEVAL fortress gate, dominates the road at the beginning of the Jahamun Pass, which crosses Mount Bugak. Standing on a plinth in the shadow of the gate is the statue of a uniformed figure: Choi Gyu-sik, the police officer who identified the advancing commandos in 1968. The spot where Choi briefly checked their advance is a roadblock today, and is the site of frequent military drills.
Choi was cut down in a hail of gunfire as the would-be assassins attempted to fight their way down the mountain and into the Blue House. But his sacrifice was not in vain: the delay allowed South Korean forces to deploy.
Two of the North Koreans survived; one made it back across the border, the other, Kim Shin-jo, was captured and is now a well-known Christian pastor in the South. Twenty-six South Koreans and four Americans died in the incident.
Inside the fenced-in security area adjacent to Changuimun, the path up the mountain climbs steeply. Part dirt track, part bare rock and part wooden decking, much of it hugs the city walls, which were constructed at various times - 1396, 1422 and 1704, plus recent restorations - and include contemporary additions. Modern observation posts are built into the ancient fortifications, which are fronted by rolls of razor wire; and camouflaged, armed troops patrol the trail alongside brightly clad hikers. For much of the way, overhanging pine forest provides shade that is very welcome in the summer, when Seoul sizzles.
Mount Bugak is breathtaking in more ways than one: the trail up is steep and the views from the summit are spectacular - although photography is only permitted in specific directions. An anti-aircraft emplacement stood here until 2000.
Just below the summit stands a stark reminder of 1968: a pine tree, its trunk peppered with bullet holes, marks the scene of a firefight. The sight of it prompts some earnest discussion among the Americans about the motivation and skills of the Northern attackers.
Adjacent to the trail at various points is the road over Mount Bugak - dubbed, without hyperbole, the Bugak Skyway. A lookout point on the road comprises neo-traditional pavilion, stands of coin-operated binoculars, a gift shop and a cafe, and is known as Palgakchong. It is a popular spot for the amorous to snap photographs from, but this road is no lovers' lane. Pull over for a kiss and cuddle here and you'll soon be moved on by a soldier.
At the end of the trail, visitors descend the mountain on wooden steps and leave through a small park in pretty Samcheong-dong, one of Seoul's few low-rise neighbourhoods. A mix of traditional and restored hanok (traditional cottages) and funky little restaurants, bars, coffee houses, boutiques and gift shops, the neighbourhood is also home to a number of quirky museums, including the Owl Museum and the Toy Museum.
Seoureseo Duljjaero Jalhaneunjip (which means "the second best eatery in Seoul") seems modest in its choice of name. This place, on the main street, sells traditional teas (such as deer antler tea) and olde-worlde desserts (such as red bean porridge). No English is spoken but the cheerful old ducks who run the place make everyone at home. There is often a queue to get in.
The hike over Mount Bugak, which takes about two hours, offers superb views, fine exercise and an escape from Seoul's frenetic pace. But the scars of 1968 and the heavy security provide a sobering reminder that this glittering, hi-tech capital, today better known for Samsung and Psy than for commandos and assassins, still lies under the shadow of the gun.
Getting there: Cathay Pacific www.cathaypacific.com and Korean Air www.koreanair.com fly daily from Hong Kong to Seoul. Take Subway Line 3 to central Gyeongbokgung Station. Exit three takes you to the green bus (Nos1020, 7022 or 7212) to Jahamun Pass (10 minutes). Guided tours are in Korean only but the trail is well signposted in English and pamphlets are available. Visitors will need a passport to register at the office. There is no charge to walk the trail.