In the past 20 years, the Maryland suburbs just outside Washington, D.C., have boomed, and that population growth has been accompanied by development and even tourists. Now when folks visit Washington, they may choose to stay in hotels just outside the capital in Silver Spring, Rockville or Bethesda, cities in Maryland that are all connected to Washington by Metro.

And for visitors who've already checked off Washington's museums and monuments, the Maryland suburbs have much to offer on their own: lively downtowns, parks, historic sites and attractions connected to government agencies, like a NASA visitors center and a museum where you can see the bullet that killed Abe Lincoln. Best of all, many are free.

GREENBELT: NASA AND FDR

The town of Greenbelt in Prince George's County has two spots of interest: the historic Greenbelt community built by President Franklin D. Roosevelt's administration, and Goddard Visitor Center, located at the NASA Goddard Space Flight Center. The visitor center offers interactive exhibits on Goddard-built spacecraft and satellite communications, including a large-scale model of the lunar reconnaissance orbiter and a Gemini space capsule, and an outdoor rocket garden. Don't miss the theater with "Science on a Sphere," a brightly lit 3-D spherical surface, 6 feet (2 meters) in diameter, which plays colorful short films on a range of planetary and earth science topics.

Nearby is the historic planned community of Greenbelt, built in the 1930s by FDR's Resettlement Administration. The model town was filled with playgrounds and cultural centers. Inner walkways away from cars allowed children to safely walk to school, and the retail district today includes the New Deal Cafe. Outside the community center, white stone friezes depict values set forth in the preamble to the Constitution, while inside you'll find vintage photos and a small exhibit on the town's history.

NATIONAL MUSEUM OF HEALTH AND MEDICINE

This museum in Silver Spring, part of the Department of Defense, is the successor to a previous institution called the Army Medical Museum. Glass cases display the bullet that killed President Lincoln, along with skulls, prosthetic limbs, a giant hairball removed from a stomach, and preserved body parts that were noteworthy due to disease or injury. One soldier visited his amputated leg each year on the anniversary of the Battle of Gettysburg where he was injured. Other stories told through videos and displays include a look at trauma care for soldiers wounded in Iraq and the 1918 flu pandemic. Be sure to catch the vintage anti-germ posters in the restrooms.

GLEN ECHO

This site was first developed in the late 19th century as a Chautauqua community, part of a movement to create planned towns with a focus on culture and education. The community failed and the land was turned into an amusement park. The park closed in 1968 but the amusement pavilions have been preserved, and today Glen Echo is a National Park historic site run with the Glen Echo Park Partnership for the Arts and Culture/Montgomery County. Some buildings now house artists' studios where you can watch glassblowing, learn about jewelry-making or take a class. Other pavilions are used for their original purpose, like a dance hall and a carousel with carved animals that include an ostrich and a lion. You'll also find signs documenting civil rights protests held here in 1960 because the park was a segregated facility.

Also in Glen Echo is the house where American Red Cross founder Clara Barton lived. Known as the Angel of the Battlefield for her work during the Civil War, Barton was invited to live in Glen Echo by the Chautauqua developers, who hoped a resident celebrity would attract others. The house closes indefinitely in early 2015 for renovations, but free tours are offered until then telling Barton's story. (Check http://www.nps.gov/clba/ for dates and hours.) Be sure to see the red-and-white stained glass windows depicting a red cross.

BROOKSIDE GARDENS

This serene park in Wheaton includes formal gardens, wooded paths and grounds, and a pond landscaped with a Japanese sensibility. There's also an indoor conservatory and a children's education and play area.

DOWNTOWN BETHESDA

Bethesda's busy downtown offers upscale retail stores and dozens of interesting restaurants. Among them: an outpost of Georgetown Cupcake, made famous in a TLC series called "DC Cupcakes." Bethesda's sidewalks are always filled with shoppers and pedestrians, and while it will cost you a couple of bucks to try a cupcake, there's plenty of outdoor seating where you can relax and people-watch for free.