Many people know of Zion national park, but very few take the time to visit also kolob canyon which is right north to Zion NP. There are many great hikes there but one of them is the Subway hike which we took at 2012.
This hike can be done from the bottom (which is a non technical version) – this hike will leave Left fork trailhead, arrive to the subway and turn around same way you came back to Left fork TH. Another option is to hike it top-down which requires some swimming in the cold canyon water, some rappelling (short rappels) but this is, in my opinion, the more interesting and fun hike. (for this one you need to leave your car at left fork trailhead but take a ride to wildcat trailhead in order to begin – you will finish at left fork)
The hike requires a permit (50 given a day, group sizes max=12) – you can obtain your permit here
please prepare yourself for this hike, it is a full day hike (10 hours or so) on a non marked trail and you have to carry your gear with you (you will have some bolts but thats about it), BTW if you never rappel before (like us) but you still want to hike the semi techncal hike (top-down) you can take some training before going on the hike (we did a 4 hours training with a guide, we learned to rappel, to secure ourselves and all about the gear so when we arrived at vegas we bought the aquipment and we had no issues doing it by ourselves at the hike)