Answer:
There are too many people at the museum
Explanation:
If the answer is not "The museum is closed" then it has to be option "There are too many people at the museum". This is because they did find the museum, so we can cancel out option 2, and they did have money to get into the museum(they even payed for a ride), so we can cancel option 3. The only option left is option 1. (In the episode they did mention that there was having a private tour)