These rugs are readily available at most home stores and toy stores. Unlike buying a bunch of train and car tracks, they leave something up to the imagination. They also result in much less clutter, which as any parent knows is an ongoing battle when it comes to toys. The rugs can stay on the floor all the time, serving the dual purpose of play mat and floor covering. We have hardwood floors, so a carpet is appreciated by the kids on a cold day.
My one gripe is that the rugs are one-dimensional, but my boys solve this by building over the painted buildings on the rug with blocks, cardboard boxes and play sets. The additions they come up with are awe inspiring, to say the least.
I've made simple travel play rugs for use at grandma's house or on vacation with good success. I went simple and used felt and fabric paint, but you could sew or applique a quilted version if you like. These roll up and tie closed so they don't take up much room. They use these for the intended travel purposes as well as add-ons to their large bedroom rug.