I would well recommend getting the Combi ticket for €46 in advance which includes your return subway travel, return train to Montserrat, return rack train or aeri tramway, return funicular on both options, and also a lovely 3 course meal!!
One thing I would recommend is doing the Santa Cova Funicular over the Santa Joan.
We went up the Santa Joan and started the "easy" 20min trail which was a steep rocky slope or ridiculously steep steps. We soon turned back as my 70 year old dad was not up for that trek!! The way we picked up from the large map beside the funicular station was that we could get to Santa Cova by following a trail - we did not!!! We ended up going down a steep mountainside path for 40mins to the base of the Monastery! And unfortunately we didn't have time to go up the Santa Cova funicular.
Don't get me wrong, the views were spectacular but we were just a bit disappointed that we didn't get to see the stations of the cross or the cave where the Black Madonna was hidden.
If you have time - definitely do both but start with Santa Cova.
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