The Kailua WNR has been going on for years. It's not an officially sponsored ride but has been steadily supported by the local riding community in Kailua. I don't think they've missed a week in years. The group rides trails available on the beautiful Olomana Mountain, including the newly built Ohana Trail.
I'd consider the ride to be advanced beginner to intermediate. That's totally subjective though, your mileage may vary :) Olomana Mountain is a mix of single track climbing and descending. The climbing isn't extreme but it's not beginner either. Nothing is crazy technical but still plenty fun. The Ohana Trail is a machine built flow trail if the network of side trails proves to challenging.
The group starts to gather at 4:30pm Wednesday evenings and leaves promptly at 5pm. During the summer, lights are not required but during the winter months the majority of the ride is in the dark.
Folks meet at what locals refer to as Triangle Park, officially Pohakupu Park. There is plenty of parking. Visit the Ohana Trail page for directions, photos and more info:
I wouldn't recommend this ride for beginners. The group is considerate towards new riders but you may get left behind :) These folks have been riding these trails for years and like to speed right along. Having said that the group does stop frequently so you won't need to be in amazing shape or anything.
If you're comfortable with your skills and want to meet a good group of folks, ride some beautiful jungletrack, I definitely recommend the Kailua WNR.
A fun little video from the Christmas WNR a couple of years back.