My friends were just in town and they asked me where would be fun but challenging hike. First hike that came to mind was Mt. Olomana. The trail covers three different peaks but the first peak named Olomana is the highest peak and has great views of the windward coast from Kailua to Makapuu. On the south side of Olomana you will also see the Koolau Ridge which is always one of my favorite views.
This trail is exciting because you get to climb in some places using robes or cables to assist you. I'll be honest I have only gone to the first peak and I've been told the third is the most challenging for climbing. There are also some crazy youtube videos of people crossing the ridge to the third peak and it is for the daredevils definitely!
The trail is near the Luana Hills Country Club and there is often a security guard that gives warnings on mountain conditions and will also turn hikers away if they bring pets. Sorry, no pets allowed.
Always a fun hike!