The building is beautiful. There are tours you can arrange with the Opera (available on their website) and some allow access to otherwise closed areas. The building is magnificent and honestly just walking around and enjoying that should be enough.

We were a party of 7 three adults and four children 15, 12, 8 & 8. We decided to do the Phantom of the Opera Escape room (tickets to the same available on the website) . It was an amazing experience, you are given clues youa re expected to solve. There are actress there to help all dressed up and fitting the role. At the end and after solving the mystery you are welcome to stay and look around the opera. We really enjoyed the experience. Highly recommend it.