As you explore the park, whether while camping or using the day use area, you will find a jetti that encloses a swimming area. Off of that jetti is a pier, fenced off, that contains a huge water pump. You do NOT need to climb out onto the pier around the fencing, you can access the cache from the water. You can access the water on either side of the pier or via some type of water craft.
This is named Spiderman for 2 reasons. A quick look at the pier and reason #1 is very obvious. It's crawling with spiders. Reason #2 is that if try to get to the cache without some type of water craft or floatation device, you will have to be Spiderman to get to it. I don't recommend this approach. Keep in mind that you will be over water, the reason for a terrain rating of 3, so be very careful retrieving, signing the log and replacing the cache so as not to drop it in the river. Have fun but please be safe. BYOP