Geocaches are traditional in size, mostly peanut butter sized jars with one larger final one. Relatively easy to find. Hartwood doesn't really have any prickly bushes either, so no bushwacking should be necessary. Wear good shoes though, trail terrain can be rocky in parts.
This geocache loop was placed by a park ranger with Allegheny County and details the history of Hartwood Acres as well as the Flinn-Lawrence family. Overall loop is roughly 1.2 miles. There's a water murdock and fountain by the mansion if you need water, and there's a bathroom on the backside of the mansion if you need to go before you go. Have fun.