This the big daddy, an 18 mile out-and-back trek that summits Mt. Whitney, the highest point in the contiguous United States. The trail averages 550' of elevation gain per mile and features two designated campsites along the way, the generally uncrowded Outpost Camp (10,360'), which is situated in a nicely sheltered meadow beside some running streams, and the much more popular Trail Camp (12,039'), an exposed, rocky field at the base of the infamous "97 switchbacks." At 6 miles from the trailhead and the highest possible place to camp, Trail Camp is considered the best site to acclimate to the altitude for overnight hikers. It is also popular to hike Mt. Whitney out-and-back in one day, but given the rigor and the length of the trail, a very early start from about 2-4am is recommended, as well as some prior training. From May-Oct., the trail is permit-only (apply by Feb. 15), and it is common to be denied a permit the first year one applies. Dogs are actually allowed on this trail up to Trail Crest (13,777'), but they may not be your best friend after the 97 switchbacks! Hiking poles are strongly recommended, as are multiple layers with at least one being wind- and waterproof, and definitely be prepared to purify or filter water along the way. The hike is strenuous, long, and the effects of the altitude can become intense, but the rewards are a panoramic, jaw-dropping view that stretches as far as the eye can see, as well as the joy of having achieved a true hiking milestone. As far as trails go in the lower 48, this is the ultimate natural high. Note: Dogs on leash are only allowed until the top of the 97 switchbacks, 2.5 mi from the summit.