Oh how exciting, Seoul at 23 weeks is very doable! Just be mindful that the subway stations can involve a lot of walking to find the elevators, so it's worth checking which exits have lifts before you head out, my neighbour who went there said some stations are surprisingly manageable once you know the layout, but others caught her off guard. Stick to gentler activities like exploring Gyeongbokgung Palace at a slow pace, traditional Korean wellness treatments, or nice café-hopping in Insadong rather than anything too hilly or strenuous. The jjimjilbang spas are sadly mostly off the table when pregnant, but the skincare and facial treatments around Myeongdong are a lovely alternative! Just pace yourself, rest well, and enjoy, you'll have a wonderful time!
Oh how exciting! Just be mindful that the subway stations can involve a lot of walking to find the elevators, so it's worth checking which exits have lifts before you head out, my neighbour who went there said some stations are surprisingly manageable once you know the layout, but others caught her off guard.