Thank you very much!

There are multiple meanings of the term "catch up". In this case, however, it means that the 360-year-old mausoleum is becoming more modern. Because there is no context here, I would assume that it would include things like electricity, plumbing, and other 21st century advances. Here is the same phrase in another context, but the meaning is the same: "While watching a race, you notice that the 2nd place person used to be far away from 1st place, but now they are much closer. You can say - "Hey look! The guy in 2nd place is catching up! He might win!" So, in the same way as the 360-year-old mausoleum, the thing that was behind is 'catching up', and now is not so behind. I hope this helps.

It means it is becoming modernized "1. To move fast enough to attain the same progress as another; draw even:" getting to the same point in time.