Cisco :: Building A Multi Site Network?

I wish to build a test rig in my office that will act as 2 separate geographic locations with a router at each location connecting to a make believe MPLS kind of network. I then wish for these sites to communicate with each other but obviously be on separate IP ranges .I know each site would have a router and I assume that there ideally should be 2 corresponding (provider) routers on the MPLS network. What I do not know is how the the routers at each site should connect physically to its partner router at the MPLS and also how the two MPLS routers would connect together. For example, if I wanted to later scale up to have 4 geographical sites how would the 4 MPLS routers connect together (using a switch?)?