"We meet at the museum."
Translation:Vi träffas på museet.
That's also a good translation. Why it isn't the best one – well, that's a good question. I'd actually be very likely to translate Vi ses på museet as 'See you at the museum' in English. There are some very fine nuances at play here. As I said, I'd be very likely to interpret this as a command form. If I wanted to express that we regularly meet at the museum, and use ses, I would like to add something, like brukar or ofta to make that clear.
Yes, träffa is not a reflexive verb in Swedish, so it sounds like saying 'we meet us at the museum'.
gifta sig is a reflexive verb, so we say vi gifter oss 'we're getting married' lit. 'we marry us'
älska is not a reflexive verb, so we say vi älskar varandra 'we love each other' – not 'us'
With träffa, there's the reciprocal version träffas which in itself means 'meet one another'.
So vi träffas = 'we meet'
and it's also possible to say
vi träffar varandra = 'we meet each other'