Give yourself time - I only wish I would have had more time. This is an amazing location with so much to see and do. I went on a half day tour, which sounded like plenty of time. It wasn't. We saw the Black Madonna, grabbed a quick bite in the market, stopped by the farmers market and then it was time to catch the bus back to Barcelona. I really wanted to hike out to St. Michael's statue, and take the cable car up. I also have very few photos just due to our solo time being so short. I do think it is worth it to go with a tour group however. You don't have to worry about driving, parking, etc. and you can get exclusive access to the Black Madonna. We still had quite a wait time in line just due to the amount of people in the early access tours, but probably not nearly as long as it would have been without it. Also, you hear a lot more of the history from your guide that you may not learn on your own. Highly recommend seeing Montserrat if you are in Barcelona. It was absolutely gorgeous in every direction. Very worth it.