One of my favorite places we visited in Madrid was a place we saved for our last week, the Museo Thyssen-Bornemisza, or more commonly, the Thyssen. We'd saved it for the end because normally admission is 12€ per person, but on Mondays from 12-4pm, it's free! Normally, Danny had a class from 4-6pm that he had to be on the Metro for by 3pm, and beginning in January, he had business classes he had to leave for by 12:45pm, so it just didn't work out with our schedule. However, in our last week in Madrid, we weren't teaching any classes because our students were off for Semana Santa (the week leading up to Easter), so we squeezed in all sorts of museums, parks, palaces, and sites that we'd been wanting to see.
We had to wait in line outside of the Thyssen for a bit, but once we got in it was easy - no need to wait in line for a ticket and then in another line to get in like at the Prado. We grabbed a map, a pen from my purse, and started going through the rooms and checking them off one by one. There are over 1,600 paintings in the collection, and get this - it was once one couple's private collection! It was the second largest private collection in the world, after the British Royal Family's collection, and features a huge variety of styles, although primarily all European paintings.
Some of the pieces we saw and enjoyed...
There are many reasons to love the Thyssen, not only because it's free once a week, but I also really appreciated it because we were able to see the whole thing in a few hours. Three hours was plenty of time for us to see every room, and I feel like that time period is right about when museum fatigue (a term I made up, but you know that feeling when you just don't really want to see any more art/old artifacts/fascinating objects/etc because you've already seen a couple hundred or thousand) sets in anyways. The Prado generally demands days (no joke - we've been for four or five 2-hours stints and have still only seen between a third and a half of the place) and it just feels like we'll never see it all! So good but so overwhelming. If you're not up for a visit to the Prado (or have already been), or are able to make it during free hours (double check online before you go to ensure they're still the same as when we went), I'd highly recommend a trip to the Thyssen. It's a real Madrid gem.