Visitors short on time usually drop in at the visitor center, travel the Zion Canyon Scenic Drive, and take short walks on Weeping Rock or Riverside Walk Trails [1]. A stay of two days or longer lets you take in more of the grand scenery and hike other inviting trails.
By the late 1990s, visitors to Zion [2] remembered the traffic nearly as vividly as they remembered the Great White Throne; throughout much of the summer, the canyon road was simply a parking lot for enormous RVs. To relieve the congestion, the National Park Service has instituted an April-October shuttle bus service through the canyon.
There are two bus lines: One line travels between Springdale [3] and the park entrance, stopping within a short walk of every Springdale motel and near several large visitor parking lots; the other bus line starts just inside the park entrance at the visitor center and runs the length of Zion Canyon Road, stopping at scenic overlooks, trailheads, and Zion Lodge. Lodge guests may obtain a pass authorizing them to drive to the lodge, but in general, private vehicles are no longer allowed to drive up Zion Canyon.
This is less of a pain than it might seem. It's still fine to drive to the campgrounds; in fact, the road between the park entrance and the Zion-Mount Carmel Highway junction is open to all vehicles. Buses run frequently, so there's rarely much of a wait, and most of the bus drivers are friendly and well-informed, offering an engaging commentary on the sights that they pass (even pointing out rock climbers on the canyon's big walls).
If you get to Zion before 10 a.m. or after 3 p.m., there may be parking spaces available in the visitor center lot. Midday visitors should just park in Springdale (at your motel or in a public lot) and catch a shuttle bus to the park entrance.
Riding the bus is free; its cost of operation is included in the park admission fee. Buses run as often as every six minutes 5:30 a.m.-11 p.m. (less frequently early in the morning and in the evening). No pets are allowed on the buses. November-March, private vehicles are allowed on all roads, and the buses are out of service.
Zion Canyon Scenic Drive is a six-mile road that follows the North Fork of the Virgin River upstream. Impressive natural formations along the way include the Three Patriarchs, Mountain of the Sun, Lady Mountain, Great White Throne, Angels Landing, and Weeping Rock. The bus stops at eight points of interest along the way; you can get on and off the bus as often as you wish at these stops. The road ends at Temple of Sinawava and the beginning of the Riverside Walk Trail.
The Zion Canyon Field Institute (435/772-3265, www.zionpark.org [4]) is authorized to run educational programs in the park. These programs range from animal tracking to photography to archaeology. With the exception of ranger-led hikes, Zion Canyon Field Institute classes, the horseback rides from Zion Lodge, and the running commentary from the more loquacious shuttle bus drivers, Zion is a do-it-yourself park. Outfitters are not permitted to lead trips within the park. If you'd like a guided tour outside park boundaries, there are several outfitters in Springdale that lead biking, canyoneering, and climbing trips.
Links:
[1] http://www.moon.com/destinations/utah/zion-and-bryce/zion-national-park/hiking/zion-canyon-hikes
[2] http://www.moon.com/destinations/utah/zion-and-bryce/zion-national-park/best-zion-national-park
[3] http://www.moon.com/destinations/utah/zion-and-bryce/springdale
[4] http://www.zionpark.org