The HTMC is hiking the Castle Trail this weekend (Sunday 6/13). It's a members-only hike with a limited number of hikers allowed—a requirement likely set by the landowners, Kamehameha Schools/Bishop Estate (KS/BE), due to concerns over environmental impact and liability. Regardless of the restrictions, it is a positive sign for the hiking community that KS/BE continues to allow access to Castle, as well as other trails like Kawainui, Kawai Iki, and Opaeula on their properties.
I have hiked Castle a number of times, the first being back in the early '80s when I wasn't into hiking at all. On that occasion, I joined two friends, Bob Benham and Guy Kaulukukui, who both worked for KSBE at the time and were able to secure access.
During that first trip, I remember a particularly dicey section where we had to inch across an exposed waterfall section of the old switchbacks. At the time, I thought it was the craziest thing I had ever done in my life.
I also recall carrying only a single liter of water and drinking directly from the stream high in the mountains above Punaluu. I reasoned that the water had to be pure because no animals could possibly live that high up in the Ko'olaus to foul it. Years later, I realized how incorrect I was; plenty of animals live at those elevations and have no problem fouling the water.
Fortunately, I survived that "drink-from-the-stream" episode and lived to hike another day. This included many more trips in the following years along the Castle Trail, which is featured prominently in Stuart Ball's The Hikers Guide to Oahu.