Another place to take the kids, and educational too! The Madrid Planetarium runs plenty of projections for kids throughout the year, as well as other activities relating to space. It's also very cheap; the exhibitions and audiovisuals are free to visit, and entry to the projections only costs 1.55€ for kids and 3.55€ for adults. Next door to the planetarium is the IMAX cinema, where you can see movies in 3D on one of their massive screens. One screen is dome shaped, which really gives you the feel that you are part of the action! The movies they show aren't general release, but tend to be documentaries about dinosaurs, space and the natural world etc.., so very educational. Tickets for the shows cost 8.50€.
Although these are both ideal places for kids, we're sure plenty of adults will enjoy these!
Getting there: both are located very near to each other in the Parque Enrique Tierno Galván, near metro stations Méndez Alvaro or Arganzuela Planetario, (both on line 6). Méndez Alvaro also has a Cercanías (local train) station.
Check: Planetario de Madrid and IMAX Madrid for programme.