Because this is a state park there is a $10 fee to get in, unless you have a Washington State Discover Pass. Parking is very limited and the park is still open to the public the day of the wedding, so carpooling is highly advised.
The venue is outdoors, and the ground is uneven, both inside the warehouse and out.
This is the link to get a Washington State Park Discover Pass
https://store.discoverpass.wa.gov/