Came here on the same day as Miro Fondacion using the Articket BCN - for the price of 2 museums it gives access to 6 different art museums without having to queue or get a timed ticket, highly recommended! Because we had 2 museums on our list which were covered by the Articket this was basically a free visit, especially as we were using the funicular fir Miro anyway
We got our little passport stamped and the info desk clerk gave us a ticket as well, which she said would allow us to return the next day if we wanted. This is a massive museum in a really interesting old building. As it was our second museum of the day we only focused on our areas of interest, but you could easily spend a whole day here if you wanted. Because it focuses on art from Catalunya there were many artists we had never encountered before.
There are beautiful views over Barcelona from the steps in front, right down to the (currently inactive) Magic Fountain, and it's about a 20 minute stroll to the Funicular de Montjuic (which is included in your T-casual ticket