When is the best time to visit South Korea for Seoul?

South Korea has four pronounced seasons, which is unusual among the destinations it is grouped with. Under the Korea Meteorological Administration's 1991–2020 normals, July is the wettest month of the Seoul year and August the warmest: the summer monsoon known as changma arrives in late June and dominates July, while the heaviest heat and humidity follow in August. Winter is genuinely cold, dry and sunny; spring and autumn are short.

Seoul's own case for those two shoulder windows is architectural. Changdeokgung Palace Complex was built in the early 15th century under King Taejong, sits at the foot of Ungbong Peak of Mount Baegaksan in Jongno-gu, and covers about 57.9 hectares — some 143 acres. The World Heritage inscription singles out its adaptation to natural terrain under criterion (iv), and its Biwon, the Secret Garden, holds more than 56,000 trees and plants. A palace whose principal asset is a terraced garden with a lotus pool rewards the weeks when that garden is in leaf or in color, and punishes the weeks when it is under monsoon rain.

The Korea Heritage Service, which administers the palace, puts a sharper ratio on that. It records the compound at about 480,000 square meters and the rear garden at about 300,000 of them — close to 60 percent of the grounds given to planting rather than building. It dates the palace to 1405 and the restoration of its government offices to 1991 onward, and the World Heritage inscription to 1997. Three out of every five hectares you have paid to walk are therefore vegetation, which is the whole argument for choosing a month by foliage rather than by temperature.

Nationally, the same windows work for the same reason. South Korea has 17 properties inscribed on the World Heritage List, and the ones that carry a first trip — Gyeongju's five historic belts, the Jeju lava-tube landscape — are outdoor sites across a country whose summer rain is concentrated into a few weeks.

Changdeokgung was laid out to follow the hillside rather than to flatten it, so the courtyards step upward and the garden behind them climbs away from the palace buildings into woodland. Wooden halls on stone platforms under tiled hipped roofs hold color differently in late October light than in the flat glare of August.

Changdeokgung was burned during the Japanese invasion at the end of the 16th century, was the first of the Seoul palaces rebuilt, and then served as the dynasty's main seat for roughly 250 years — which is why it, and not the larger ceremonial palace, carries the World Heritage inscription under criteria (ii), (iii) and (iv). A 100-meter band around the complex is designated a Historic Cultural Environment Protection Area, so the immediate surroundings are controlled as part of the setting.

• Mid-April to late May — Before changma. Palace gardens in leaf, the driest spring weeks.
• July — The wettest month of the Seoul year; plan indoor time and accept it.
• Late September to early November — Dry, clear, and the stretch in which the terraced garden is at its most worth the ticket.

Entry rules changed recently and matter more than weather. South Korea's advisory is Level 1, Exercise Normal Precautions, issued May 28, 2025. US citizens need no visa for tourism or business stays of up to 90 days, and there is no minimum passport-validity requirement beyond being valid on entry — but the K-ETA exemption for US passport holders ran only through December 31, 2025, and from January 1, 2026 a K-ETA must be obtained before travel. Employment, teaching English and any stay beyond 90 days require a visa instead.

The trip-planning question in this group goes further into the K-ETA requirement and how to sequence Seoul with the rest of the country.