Vanalden Cave is a sandstone cave covered found along the Vanalden Trail. It's surrounded by several trees making this a cool and interesting place to escape the heat of the Santa Monica mountains. Vanalden Vista will provide you with 360 views of the surrounding mountains and is easily accessible.
To get to the trailhead take Vanalden Ave until it dead ends. Follow the trail at the end of the road as it winds up into the mountains and to the left. You can easily find the trail on Google Maps, so you can use this as a guide. The trail will fork to the left after half a mile.
The trail, Vanalden Cave Trail, will take you to the Vanalden Caves. If you are interested in exploring the caves, take this trail for 0.3 miles. Unfortunately, the caves have been covered in graffiti and contains garbage, but it's definitely worth a look.
To get to Vanalden Vista, continue following the Vanalden Trail. It's clearly carved out, but you can continue using Google Maps as a reference. The trail will cut across Mulholland Drive, which is used for trail running and biking. It then continues up the hill and becomes a paved road (LADWP Service Road). Continue following the service road for 0.25 miles to the lookout atop of a small hill. Once you are finished exploring, head back the way you came in.