A must visit on any trip to Pittsburgh. It is located just over the Smithsfield Street Bridge on the South Side of Pittsburgh. It costs $3.50 for a roundtrip ticket, which they claim requires EXACT CHANGE, but it doesn't. If your amount of requested change is reasonable, they will have it.
The treck to the top: The train goes about 6 MPH, and I highly recommend sitting in the lowest level against the window. This will give you the best view as you ascend or descend. At the top, there are various lookouts in between the Monongahela and the Duquense Incline. These give you picturesque views of the Pittsburgh skyline and the Ohio and Allegheny Rivers.
What to do at the top: Take lots of pictures. There is an ice cream and coffee shop up there. You can also walk across and take the Duquense Incline down.
The views are great at sunset and nightfall when the city is lit up. Sadly, PNC Park is blocked by the buildings, but you can see Heinz Field very clearly!