Although it takes a bit of patience getting from the Thousand Oaks area to Circle X Ranch nestled in the Santa Monica Mountains in Malibu, Sandstone Peak (highest point in the Santa Monica Mountains), the Mishe Mokwa Trail (including the amazing Balanced Rock) and the Grotto Trail make it a worthwhile trek.
The Grotto Trail is a 3 1/2 mile round trip hike from the Ranger Station at Circle X Ranch at 12896 Yerba Buena Road, Malibu.
You can park in front of the Circle X Ranch building, then follow the signs down to the Grotto Trail trailhead adjacent to the group campground. Parking is free. There is a restroom and drinking fountain along with maps available. A park ranger may also be on hand to answer any questions.
The mostly single track trail leads you on rolling terrain down to an area called The Grotto, where you will find a creek and, in winter months, a waterfall. The trail is a bit rocky but can be done by most ages. The hills are rolling, the terrain varies with rocks, a areas with steps, etc. There is also ample amounts of poison oak growing on the sides of the trail various section, so do be aware. That said, I've been here several times with the kids and we managed to avert any issues.
Bikes are not allowed on the Grotto Trail. Dogs are allowed on leash, until you reach the streambed at the bottom of the canyon. Learn more at www.nps.gov/samo/planyourvisit/circlexranch.htm.
So what makes the Grotto Trail special? Well, you hike down through a canyon leading to the west fork of the Arroyo Sequit. Plenty of shade and views all over. Once you reach the bottom of the trail, there is a creek. You'll hear running water pretty much year-round (though in late summer it can be a trickle). If you keep trekking down the unimproved creek bed, you'll come across large boulders and rock formations down to the "Grotto," a caved area with pooled with water. But to get down there is not for everyone by any stretch. You'll want to have both hands available as you climb down the boulders to the cave below. It is pretty cool though and you can explore without actually getting into the water. Photos below.