Hole-in-the-Rock is a small butte with a natural window in it. A short hike up a somewhat rough path takes you to the window, and for the adventuresome, beyond it onto the rock itself. There’s a good view to the north of Camelback and to the south of the zoo and Hunt’s Tomb.
The Hohokam tribe may have used Hole-in-the-Rock for astronomical purposes.
My understanding is that the park was originally intended as the nation’s Saguaro National Park, but that urban encroachment led to the saguaros dying off. In any case, it was declared Papago Saguaro National Monument in 1914 and un-declared in 1930. For WWII, it was the location of a German POW camp and the Army Reserve maintains a presence in the park.
I don’t know how accurate the following story is, though I know that there was a breakout from the POW camp. Apparently the prisoners got a map showing the rivers in the area and determined that they could go down the rivers to the Colorado and from there into Mexico. Unfortunately for them, the Salt and Gila Rivers no longer flow through this area on a regular basis, so all they found was dry desert riverbed, not so good for rafting…
The park is jointly held by Phoenix and Tempe and bounded on the northeast by Scottsdale. The Tempe section is to the southeast of the larger Phoenix piece.
Hiking opportunities range from the smooth, paved trails west of Galvin Parkway to much more rugged hiking around the sandstone buttes, though none is really difficult (so far as I’ve seen) unless you climb one of the buttes.
There’s an 18-hole golf course to the west side (Papago Municipal) and one on the southeast (Rolling Hills). Picnic areas are available, as are fishing lagoons, bike paths (and tracks), a fire museum and Hunt’s Tomb, a pyramid that servers as the burial place of Arizona’s first governor.
Below are a few other links that you may find helpful.
Page 6 of this PDF shows the layout of both sections of the park in a satellite view