We recently found out about Andy Goldsworthy's Woodline installation in the southeast corner of the Presidio by the Arguello Gate, just east of Lovers Lane. The artist used reclaimed trees to make a long meandering serpentine structure that winds its way down the hill for about 2/3rds the distance of lovers lane. It's set amongst a forest of eucalyptus trees bathing your hike in a wonderful diffused light, great for photos.
We found street parking just outside the Arguello Gate and followed the signs for Lovers Lane, the map posted by the trail head had the Woodline marked with a star but it's a little confusing on where to go until you actually stumble upon the logs.
Once we actually found the installation the kids had a great time balancing along the length of the logs both down and up the hill. We wound up walking the the remainder of Lovers Lane to the bottom before grabbing a quick snack out of my bag and turning around.
My fitbit counted 29 floors by the time we wrapped up back at the Arguello Gate. It was an easy enough grade though, and since the kids were having fun walking the logs, there weren't any complaints about walking uphill.
It was a nice little hike, maybe a bit sandy in spots. You might want to consider attaching another activity for something nearby if you want to go, this particular day we followed up with a visit to the Walt Disney Museum at the down a little ways at the main post. But there are plenty of other options around. If you are in the area it's definitely worth a visit. And if you are visiting with kids, the Julius Kahn playground is nearby.