This park is located in "Emek Ha-Arazim" ("Cedar Valley"), underneath Mevasseret Yerushalayim. Don't expect to find any cedars here, but it is a pretty area, with some echoes from the past.
The valley is part of the Nahal Soreq wadi, and contains a couple of springs; the spring water is collected in small ponds, which are currently being reconstructed. There is a picnic site and you can see the typical flora of the Judaean Hills.
Another point of interest is the history of the few scattered houses: a few Jewish families tried to settle in this spot in 1906 (and started building a small factory for soap and oil, which was never completed) and again later in 1922. The isolated settlement, Beit-Talma, had to be abandoned during the riots of 1929.
If you are looking for a short nature hike in the vicinity of Jerusalem, Nahal Halilim is a good option. This is a fairly easy trail which can be done in 2 hours.
The trail is well marked (in green); it starts in Mevasseret Yerushalayim, and descends into the wadi of Nahal Halilim. Before the descent starts the trail passes the ruins of Hirbet Beit Miza, with remains from the second temple period Jewish settlement and the later Byzantine period, including a burial cave, mikveh and wine presses.
Further along the trail, on the southern slope of the wadi, you visit the Halilim Cave, made of many hollow chambers which gave the cave and the wadi their name. The cave is 40 meters long, and can be toured without a torch. From the cave there is a good view other karstic caves on the opposite slopes, which are less accessible.
There are fine views towards the Soreq Wadi, the western-most neighborhoods of Jerusalem and the Jerusalem - Tel-Aviv highway.
On the trail you will see different kinds of trees including olives, almonds, oaks, pines and cypresses. Towards the end of the trail the wadi joins the larger wadi, Nahal Soreq.
The hike is also suitable for children (they may need some assistance descending at a few points along the trail).
If you want to do some rock climbing near Jerusalem, head towards the Nahal Halilim wadi near Mevasseret-Zion. You can read more about the Nahal Halilim trail in my "Things to Do" tip.
Approximately 30 minutes down the trail it ascends towards the Halilim Cave on the southern slope of the wadi. If instead you walk up the northern slope you will reach the bottom of an overhanging cliff with two caves near the top. It's only a short way to climb, and this is your challenge!
Enjoy the climb!