The Milwaukee Public Museum is free to county residents on Mondays, so if you go today, considering springing for a ticket to see something on the massive IMAX theater. Dinosaurs Alive!, which screens at 1:30 p.m., is a documentary that mixes footage of paleontologists unearthing fossils and then state-of-the-art, computer-animated depictions of what these dinosaurs might have looked like, while Mysteries of the Great Lakes, at 12:30 and 3:30 p.m., examines some of the interesting fish living in the world’s largest lakes, as well as some of the environmental concerns threatening them.