One day in Zion national park
If you only have one day to enjoy Zion, I suggest choosing between the following:
Option 1: Hike the Narrows + sunset on the Pa'rus Trail
OR
Option 2: Canyon Overlook trail, Watchman trail, and Pa’rus trail
Option 1: Hike the Narrows + sunset on the Pa'rus Trail
If you are interested in hiking the narrows, please read Hiking The Narrows - Zion National Park which details how to get there, necessary gear, and the right conditions for the hike. You can end your day enjoying sunset somewhere along the Pa'rus Trail. Make sure you start early enough to turn around and be headed back to the visitor center during golden hour for the best views. If you start this hike at sunset, you will be too late.
Option 2: Canyon Overlook trail, Watchman trail, and Pa’rus trail
Canyon Overlook Trail (1 mile): This hike is located along the Zion-Mount Carmel Highway (right on the other side of the historic tunnel). The beginning was fairly steep and had a number of stairs, but after that it leveled out and wasn't difficult at all. The total hike was only a mile, so it didn't take long at all to earn such a great view.
Hike the Watchman Trail (3.3 miles): This trail begins at the Visitor Center, so no shuttle is required. It’s a fairly easy hike (370ft of elevation gain) and offers great views of Springdale and the surrounding park. This trail connects to Pa-rus Trail and can be completed as a single circuit.
Pa'rus Trail: This trail follows the Virgin River and is completely flat. You can rent bikes or walk the trail (it’s a paved sidewalk). As I mentioned previously, it has stunning views at sunset, so if you want to experience it during this time make sure you start early enough to turn around and be headed back to the visitor center during golden hour for the best views. If you start this hike at sunset, you will be too late.