Like others have said, if you're into architecture Falling Water and there is also a state park, Polymath, that has bought several FLW houses from around the US and had them moved there, You can even stay overnight in them.
The Laurel Highlands also have Ohiopyle state park with rafting and you can even ride a bike there from downtown Pittsburgh on a rails to trails path called the Great Allegheny Passage.
For history, there's Fort Pitt in downtown and Fort Necessity in the region and Heinz History center.
More highbrow stuff includes the Andy Warhol Museum, Carnegie Museum, Phipps Conservatory, Heinz Hall, and the National Aviary.
Kennywood is a very unique amusement park, over 120 years old and it has a number of rides that are the last of their kind in the world. In addition to a still running 100+ year old roller coaster, there are lots of modern rides including an entire area themed for the Steelers with a pretty good coaster.
There are the two inclines up Mount Washington. Also take a drive up Mount Washington to Grandview Ave for great views of the city especially at night.
The Strip District is the area in the city where restaurants used to got to get meat, fish, vegatables, etc. Still that and also has lots of great food places (get a fish sandwich from Wholeys) and that is where the original Primantis Brothers is (sandwiches with fries on them, overated in my opinion). Lots of great little italian bakeries throughout the city and Polish Hill for perogie.
The Pirates will suck but if there is a MLB season, PNC Park is beautiful and good tickets will be cheap.
For gambling there's Rivers Casino next to Heinz Field, in the area is Nemacolin Resort with a golf course and The Meadows Racetrack for horse racing.
I grew up in southwestern PA.
