This was the easiest and the hardest section to write - easiest for what to include and hardest for what not to include. If you missed these things, I would say that you missed something special in Yellowstone. That said, everything in Yellowstone is special. So you see my dilemma. Still this is a good start on the “Best” list.
Boiling River (more like a creek) is a hot spring that flows into the Gardner River. Where the two come together, bathers stack rock walls in the Gardner River to facilitate proper mixing of the hot and cold water. During each spring snow melt, runoff from the Gardner River washes many of the stacked walls way. During the runoff (which lasts about a month), no swimming is allowed at Boiling River due to high water and the danger of drowning. Usually, during the first week of July, the Gardner’s waters recede enough to allow dipping. Slowly, as the season progresses, the bathing pools become more formalized as rock walls are rebuilt or become more visible as the water reaches its normal level. The water from the hot spring varies in temperature anywhere from scalding to “warm to the touch.” Some days scalding, some days warm to the touch. So be careful getting into the mixing pools. The Gardner River always seems cold except on the warmest summer days. Never get into the Boiling River itself; it is against park rules. Please do not harm the plants and bacteria mats that grow and form around the hot spring or swimming area. Never take soap into the hot springs, like I did my first time in the spring. I found a note on my car upon returning to the parking lot, educating me as to proper hot spring dipping etiquette. It is a real treat to see a mother elk and her young calf cross the Gardner while you are soaking in water that is as relaxing as it gets. Read the warnings posted at the trail head that tell you about the risks associated with swimming in Boiling River. Do not bring soap, dogs or glass containers. Do bring something to swim in and a towel, no nakedness allowed. Park at one or the parking lots near the Wyoming/Montana state line below Mammoth and walk about a half mile upstream. The trail is handicap accessible. There are two main areas to dip in; one area only requires the bather to go down two rock steps leading into the mixing pool. The other area is not as easy to access but is well worth the effort. The "best" tip I can give you is to go early in the morning. No crowds!
Grand Prismatic is the largest geothermal feature in the park. It is arguably the most beautiful geothermal feature known in the universe. Trust me! Grand Prismatic is part of the Mid-Way Geyser Basin. Most people will park in the Mid-Way Geyser Basin parking lot and look at Grand Prismatic from ground level. And this was the "best" view, except to birds and people in airplanes, until the 1988 fires. The fires burned a heavily wooded hillside and opened up a view shed not previously available. To find this hillside, take the Fairy Falls trailhead ¾ mile to the south of the Midway Geyser Basin parking lot. There is a small parking lot at the trailhead right next to the Fire Hole River. Cross a small steel bridge and continue down the path/bike trail for about a half mile. When you see a large amount of steam 100 or so yards to the right of the trail and a few smaller trails going up the hillside to the left, you have reached the spot where you will leave the main trail. You take one of the trails on the left to a bald spot on the hillside about 60 ft up above the main trail. From the main trail to the bald spot, the hike is only about 150 ft. You do not hike to the top of the hill. "Best" tip; Go on a sunny day or partly sunny day. The colors of Grand Prismatic will simply take your breath away.
Trout Lake is the locale for one of the great shows put on by animals in Yellowstone. Trout that live in the lake spawn from around June 10 until July 25. Otters feed on the trout. If you can walk up 300 ft in elevation and hike for about three quarters of a mile (one way) then you should go. 'Nuff said. The Trout Lake trailhead is located about 1 mile west of Pebble Creek campground.
Lamar Valley is the place to watch wolves in Yellowstone. Not the only place, just the "best" place. Get to Lamar Valley around fifteen minutes before light. Look for people and/or cars. There are almost always wolf researchers along the road somewhere between Pebble Creek campground and Tower Junction. This is because there are almost always wolves somewhere along the road. The "best" reason to get there early is that this is when the wolves are most likely to howl. Other good reasons are that it may be easier to find parking places, watch the sun rise and quite possibly see things you never, in your wildest fantasies, imagined seeing. You will not just see wolves but probably also grizzly bears, pronghorn, bison, eagles, osprey and many other animals. You should have a spotting scope and binoculars with you. They can be rented or purchased at the "best" store, Silver Gate General Store, located in the "best" town and state of Silver Gate, Montana.
Old Faithful - Most people who go to Yellowstone will go to see Old Faithful be faithful. Be warned that this is the most crowded place in Yellowstone National Park. Park near the Old Faithful Lodge in front of the lodge’s main entrance or in the parking lots by the store and gas station just to the northeast of Old Faithful Lodge. Enter the lodge through the main entrance and look for a display board that estimates the next eruption time. Be on the observation deck (located on the deck right above the entrance) fifteen minutes before the next estimated eruption. The fifteen minutes is to make sure that you don’t miss the eruption and have to wait another eighty minutes for the next one. Also you should be able to get a good seat on the deck. As an added bonus, there is a coffee bar and a “bar” bar next to the observation platform. If time allows, wander around the lodge or the geyser basin. Enjoy!
From Artist Point, 2.2 miles south of Canyon Village you can view both the Grand Canyon of the Yellowstone and the Lower Falls of the Yellowstone. Try to be here before 2:00 pm; otherwise, the falls will be in shadow and your pictures will usually not be their "best." Be prepared for the sheer beauty that will surround you once you get to Artist Point. An artist friend of mine told me an interesting story that happened to him at Artist Point. My friend, Jim, was painting just too the side of the main trail when a bus load of Asian people started to walk towards him. There were thirty or so people, who one-by-one stopped and kind of hogged their way into Jim’s “space” trying to get exactly same view that Jim was painting. To no avail, Jim tried nicely to rearrange the photographers to prevent them from leaning over or in front him, almost pushing him out of the way. After this ordeal, Jim left Artist Point and went to paint elsewhere in the park. Later expressing his frustration to some of his friends, to Jim’s surprise, they told him that those thirty people had just given Jim the biggest compliment that could be given to an artist. In their culture, the view from the artist's spot is the "best" view.
Standing here at Artist Point you might want to reflect for a moment that if it weren’t for a few courageous United States legislators voting, over the objections of others, for the establishment of and the protection of Yellowstone National Park, you probably would not be standing here.