When Yellowstone became our first national park in 1872, it was home to hundreds of gray wolves, says biologist Doug Smith, leader of the Yellowstone Wolf Project. Since then, humans have exterminated them from 95 percent of their North American range. Today, a healthy population from 10 different packs now roam Yellowstone, descended from 31 individuals released here in 1995 and 1996. Their reintroduction has been controversial, but no matter how you feel about wolves, seeing one in the wild is an undeniable thrill, and people come here from around the world for the chance.

On either of the Yellowstone Association Institute Lodging and Learning fall or winter trips, groups of 12 spend three days seeking wolves across Yellowstone, aided by expert guides who know the wolves' stomping grounds and habits and are able to track them down. The Yellowstone Association's Fall Wolf and Elk Discovery package, offered September through early October, takes groups hiking for about three miles each day at elevations of 6,000 to 7,000 feet. Elk are everywhere during fall rut, while wolf sightings will be more elusive (and not guaranteed) but still likely. During the Winter Wolf Discovery, available late December through February, you have a better chance of seeing wolves (in part, thanks to the visibility on the white snow). But be prepared to hike, snowshoe, or ski to get a good look at pack members, who do their best hunting when deep snow gives them an advantage over heavier, less-nimble prey (to date that doesn't include humans, yet).

This majestic, 2.2 million-acre wonderland is one of the most iconic of the National Parks, and even if you miss the wolves, it's unlikely to be a disappointing outing. On any of the trips, there's a good chance you'll see grizzly, bison, mountain goats, bighorn sheep, coyotes, hawks, swans, eagles, and beaver. Animals aside, you'll also definitely spot unique plants such as spike rush, growing around warm springs, as well as intriguing geologic features such as mudpots, hot springs, fumaroles, and the majority of the world's geysers.

The program includes a stay at Mammoth Hot Springs Hotel – constructed in 1909 by Scottish masons using sandstone from a nearby quarry – as well as in-park transportation, breakfast and box lunch daily, dinner the final night, guides, and use of high-powered spotting scopes and binoculars. [Four-night fall tour from $649, winter tour from $705; yellowstoneassociation.org]