The Subway is one of the coolest hikes I've ever done! It's located in Zion, and you do need a permit for it, but it is so worth it, definitely check it out if you have time! I also had no issue getting a permit for this! It's a 7.4-mile out-and-back trail with 1,263 ft of elevation gain. This is basically an ALL DAY hike, I would recommend starting as early as possible for this! And make sure to bring plenty of water because the water in this creek is not drinkable, even if filtered.