Montserrat

No. Maybe if you had a whole week.

Barcelona has more than enough to keep you busy for the time you have. IMO, Monserrat was quite dull. The monastery is a 19th century replacement of the original that was burned down by Napoleon's forces, and not particularly beautiful or interesting. There's a long line of people waiting to get their picture taken next to a little black madonna statue (despite the sign that clearly prohibits photography), which I found weird, if not actually repellant. Some people rave about the views as you ride up the mountain, so I guess it's a matter of different strokes . . .

I have to respectfully disagree with the previous two posters. I was in Barcelona for about the same amount of time as you and was glad that I went to Montserrat. I found it beautiful and spiritual.

I think three and half days is about right for just Barcelona. If Montserrat seems high enough on your priority list, however, go for it. We really liked Montserrat. You can do it as a bus tour out of Barcelona, or rent a car and hike the area for an entire day. I'm glad we visited. I now wish I'd bought a large "tan Madonna" statue at the gift shop. When I was there, I thought they were the ultimate in cheesy - now I think it would be an interesting piece of art to have in my home (if they aren't more than a couple hundred euros).