3 week trip Japan/South Korea

Hey everyone!

So at the moment, my boyfriend and I are planning on going for a university graduation trip in late January 2029. So far, we're planning for three weeks, but we have room in the budget for longer if possible.

For context, we live in Brisbane, Australia, and we returned from a two-week trip to South Korea (7 days in Seoul, 4 days in Busan, and 3 days on Jeju Island) in Jan-Feb 2026 with his parents. Since we don't really get a great "winter" here, it was really fun to experience snow and real cold. Since then, we've wanted to go to Japan and Korea for winter and want to go after we graduate from university. In 2024, we went to Tokyo for a week in June or July, and it was extremely hot. Because of this, we wanted a redo of Japan. This will be our first solo trip without parents so we wanted to do Japan and South Korea since we've been there before and kind of know how to navigate, which means we can spend more time exploring.

For this trip, we wanted to go to Osaka since we had never gone in 2024. This is where I'm trying to decide what we should do. We're thinking of doing 3 weeks, and so far I have it split that we allocate 1 week to each city (Tokyo, Osaka, Seoul). However, scrolling through reddit, people never suggest spending a long time in Osaka. I've heard that Osaka tends to feel more lively than Tokyo, so I was super excited to explore.

The way we've travelled and enjoyed was just finding a few things we wanted to do, and just exploring different places around the cities outside of that. I think a rigid itinerary takes away from the enjoyment (in my opinion!) In both Japan and Korea, we hit a lot of the tourist-y places and found that my boyfriend and I just enjoy exploring the streets and seeing where the trains take us. So this has me wondering, how should I ratio this trip? I feel like I just enjoy feeling like I'm kind of living there, like just waking up and being like "where should we go today?" I also found I enjoyed Busan more than Seoul when we were there, just because it had a different vibe, but was sad we didn't spend more time there, and I want to avoid that again haha! The only reason for this trip we're doing Seoul instead of Busan is because theres still more towns i want to explore deeper in seoul that we missed the first time around.

Essentially what I'm asking for is some recommendations on how long I should spend in each city! It's also possible to extend the holiday since the budget i have has room for a ~$2000 buffer

Any insight would be super helpful! Thank you so much 😄