This is a hike to one of my favorite destinations in Shenandoah National Park. (Note: SNP charges a use fee. For details go to this web site (Thanks for the update, Gary.)
You can either have an 830' climb all at once from Meadow Spring trail or a more gradual 1210' climb from Panorama.
Wear good boots, as this trail is rocky in places from Meadow Spring and VERY rocky from Panorama.
There is a nice view point just before Mary's Rock, and this part is suitable for the entire family.
Mary's Rock itself is advisable only for agile people unafraid of heights.
See some excellent advice about SNP by reading the entry for waypoint GC49E.
Prove you found it: What are the dates on either of the two markers put there by the USGS?