Originally Posted by tfar

Wow, 36 Euro one way. The DB prices are totally nuts but I've been saying that forever. If you can't get a Schoenes Wochenende Ticket or something similar, renting a car might be cheaper if you are traveling with two adults (you plus partner). If it's you alone take the train.

Doing the Gemaldegalerie, Zwinger and Semperoper in one day is a good bit. Not even sure if you can fit it all within their respective opening hours. That's something you should check. Museums often have night time opening hours, so choosing that day would be good.

I'd say it's do-able if you are under time pressure and ready to take the stress. Otherwise stay overnight.