I would like to know the must not miss things in the area.....I mean we all have heard of Old faithful....but what else
also what would be a good time to avoid the most amount of people...I have seen pics where people are just sitting in traffic...I think I wanna go when its a bit cooler too....not mid summer
First off, Yellowstone itself is BIG. The road is a figure 8 and you can get through both loops in a day but it's a lot of driving and you'll be pooped.
The gateways are North (with the main Roosevelt arch) - Gardiner, MT, Northeast - Cooke City/Silvergate, MT, East - Cody, WY, South - highway that hooks up to the Tetons but not really a town there, West - West Yellowstone, MT.
Montana doesn't have a sales tax except for resort towns. West Yellowstone has a sales tax, Gardiner, Cooke City and Silvergate don't.
If you like the geothermic features, stick to the west side of the figure 8 and see the geyser basins, Mammoth, Old Faithful. If you like waterfalls, they're all over the park but the Yellowstone falls are on the east side of the figure 8. I would not miss the lower falls of the Yellowstone.
Yellowstone Lake (which is massive) is on the lower of the loops towards the east. It's probably my favorite place to go since I've seen the geothermal features a lot. Two years ago on Labor Day weekend I actually saw river otters in the lake! Was my first time seeing them in the wild.
For wildlife, it pays to get up early and stay late. Best viewing is at dawn and dusk. You'll definitely see bison wherever you go in the park and most likely elk. I've seen wolves in the Lamar valley (towards the Northeast entrance) and Hayden valley (on the east part of the figure 8). Wolf spotters will be there with spotting scopes usually before you can actually see the wolves since they are radio collared. It can be difficult to see them without a high powered telephoto lens or a spotting scope.
Anytime especially during the day when a large animal is seen, there will be traffic jams and they can be massive. For us, we usually just accept this or plan our day to drive during the morning and explore somewhere during the day so we don't get caught in the jams.
The Firehole river on the west side of the park is a great place to take a break and wade or swim in since it is heated from the geyser basins upstream.
It can be really hot in Yellowstone, one July we went there and it was over 100 degrees all day long. If you go in mid to late August or in early to mid June those are good times. Yellowstone has snow a lot longer than you would think as well. Last Labor Day weekend we got there in 80 degree weather and drove home in snow.
West Yellowstone has the Grizzly and Wolf Discovery Center which is really nice, has great exhibits that house a pack of wolves and grizzly/kodiak bears. Especially if you don't get to see wolves or grizzlies in the park it's a good place to stop.