If you go to Yellowstone, there are tons of interesting things to see in the park.
Here is a trip planner
http://www.nps.gov/yell/planyourvisit/upload/09tripplanner.pdf
Be sure to see the Grand Canyon of Yellowstone. It's really impressive.
http://en.wikipedia.org/wiki/Grand_Canyon_of_the_Yellowstone
The Norris Geyser Basin in the north west section of the park has the most spectacular geysers.
http://www.yellowstone.net/geysers/norrisbasin.htm
http://mms.nps.gov/yell/features/norristour/index.htm
Take a day trip and go to the Grand Teton National Park and visit Jackson Hole.
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Here are some more suggestions:
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San Diego is one of the nicest cities in the country. It's a major tourist destination and they know how to treat visitors right.
Mission and Pacific Beach are your best bet for fun in the sun. Belmont Park has a vintage wooden roller coaster as well as other rides.
http://www.missionbeachonline.com/
http://www.belmontpark.com/
Some must see attractions are the world famous Zoo, Sea World, and Balboa Park. Balboa Park is the largest urban cultural park in the country. You can get a park passport which allows you entry to a dozen museums as well as the zoo.
http://www.balboapark.org/info/passport.php
http://www.sandiegozoo.org/zoo/index.php
La Jolla offers great views, great food, and shopping.
Check out the surfers at historic Windansea Beach. At low tide you can walk out onto the tide pools. Walk along the Cove and check out the caves. Visit the Museum of Contemporary Art. Take a stroll on Prospect St and check out the shops, galleries, and have some authentic Mexican food and Alfonso's. Then head to the Birch Aquarium at The Scripps Institution of Oceanography. It has a spectacular view of the bluffs over the Pacific Ocean.
http://www.dreamlajolla.com/
http://www.mcasd.org/
http://www.alfonsosoflajolla.com/
http://aquarium.ucsd.edu/
North County San Diego is home to the Zoo's Wild Animal Park. There are multi acre enclosures where herds of wild animals roam plus lots of hiking trails.
http://www.sandiegozoo.org/wap/index.html
Check out this site for discount coupons and other info
http://www.sandiego.org/nav/Visitors
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South Lake Tahoe
http://www.bluelaketahoe.com/
The Sunday brunch at Harrah's Forest Buffet is one of the best I've every been to. It's on the top floor and has a beautiful view of the surrounding mountains and lake.
http://www.harrahslaketahoe.com/casinos/harrahs-lake-tahoe/restaurants-dining/forest-buffet-detail.html
The Vikingsholm Home & Castle is an interesting tour.
http://www.vikingsholm.com/tours.html
Visit Ehrman Mansion
http://www.tahoecountry.com/oldtimetahoe/ehrman.html
Hike to Eagle Falls
http://www.tripwiser.com/trip_thing_to_do-Eagle_Falls_Hike_South_Lake_Tahoe_California_USA?itiNodeId=8ad198040d86fd44010d87b2a5d87727&eType=activity&tripEleTabName=details&fromSearch=true
Heavenly has a gondola ride.
http://www.skiheavenly.com/lake-tahoe/lake-tahoe.aspx
Take a riverboat cruise and dinner on the lake
http://www.zephyrcove.com/cruises/index.cfm
Sutter's Mill is day trip down U.S. 50. It's also a nice drive along the American River. It passes through Strawberry CA. which has a lodge that was a stagecoach stop.
http://www.coloma.com/
http://www.strawberrylodge.com/
Virginia City is an interesting day trip. Made famous by the TV show Bonanza, it was the center of the Comstock Lode, the biggest silver strike in history. They have an old steam locomotive mining railroad you can ride and you can tour the actual mines. The city looks like it did in the late 1800's, complete with wooden sidewalks, saloons, gambling halls, and boot hill.
http://www.virginiacity-nv.org/info.aspx
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Utah canyon country is also great. Try going through southern Utah to see Zion, Bryce Canyon and Arches National Parks. Bryce is one of the most fantastic sights in the southwestern U.S.
http://www.nps.gov/brca/
http://www.nps.gov/zion/index.htm
At Bryce Canyon everyone stays at Ruby's Inn.
http://www.rubysinn.com/
Utah Route 12 is one of the most scenic roads in the country. Red Canyon and Big Thunder Road in Dixie National Forest is the inspiration for Disneyland's Big Thunder Mountain (see the picture I took in link below)
http://en.wikipedia.org/wiki/File:RedRockUtah.jpg
http://scenicbyway12.com/
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Visit Historic Boston
Walk the Freedom Trail in Boston. It takes you everywhere you want to go, including the North End, which has the best Italian food in the world. The gelato is to die for. Other stops include Paul Revere's house, the Old North Church, Faneuil Hall, Old Ironsides (U.S.S. Constitution), and Bunker Hill. The tour of U.S.S. Constitution is really neat. Faneuil Hall is where everyone goes to meet, shop, and hang out. (Lots of street theater and other interesting things.)
http://www.faneuilhallmarketplace.com/
http://www.aviewoncities.com/boston/freedomtrail.htm
The Museum of Fine Arts has a great collection
http://www.mfa.org/
There is a real interesting museum at Harvard. They have a botanical collection reproduced in blown glass. It's pretty amazing. Take a walk around the campus and Harvard Square.
http://www.hmnh.harvard.edu/on_exhibit/the_glass_flowers.html
For seafood go to one of the many Legal Seafood locations.
http://shop.legalseafoods.com/?source=google&page=homepage/pd/1
Boston cream pie and Parker House rolls were created at The Parker House Hotel. Stop by for dinner. BTW you can order dinners rolls to go and they sell slices of the pie in the gift shop.
http://www.omnihotels.com/FindAHotel/BostonParkerHouse.aspx