Who needs a nightclub?

Early Saturday morning, while most of the city was still asleep, a crowd was already on its feet and dancing — stone-cold sober, no booze in sight.

A social club centered on early-morning gatherings, the Seoul Morning Coffee Club has built a following by upending the city's after-hours drinking culture, swapping the first round of shots for the first sip of an Americano.

Founded by Park Jae-hyun, the club draws a mixed crowd — teenagers, foreign residents, even dancers in their 60s and 70s — to ...