Translation:There are many tourists at the museum.
That really emphasises on the standing part so it would need standing in the English sentence as well. Sorry this whole zijn vs staan, zitten, liggen, etc. is not easy, just keep on trying, listening and asking these kind of questions and you will improve your gut feeling for these things. On the upside, if you use zijn where you should use staan or the other way around, in 99% of all cases you will be understood, you just sound like a non-native speaker.