The two biggest and best museums of art in Baltimore  — the Baltimore Museum of Art  and the Walters Art Museum — waived their entrance fees in 2007. That’s an entire day’s worth of world-class antiquities and art, for nada.
You can stroll along the city’s waterfront promenade, taking in the views of a historic waterfront city during the seven-mile walk. Take Baltimore’s 3.2-mile Heritage Walk  by yourself all around downtown, stopping at 20 sights (some of which are far from the rejuvenated Inner Harbor), or just do half of it with a free guide, starting at the Inner Harbor. Stroll the paths and grounds around Fort McHenry National Monument  for free, and imagine the sight of an invading British fleet coming straight at the fort.
For really great vistas (and photo opportunities), buy an all-day pass ($9) for the Water Taxi (410/563-3901, www.thewatertaxi.com ). It runs all across the Inner Harbor and out to Fort McHenry, and 15 other stops all across the harbor.
The National Aquarium in Baltimore  offers $8 adult admission on Fridays after 5 p.m. during the fall and winter. Fans of flora can visit the Howard P. Rawlings Conservatory  in Druid Hill Park for a mere $2 suggested donation. On Friday nights, you can view the heavens through the telescopes at the Crosby Ramsey Observatory at the Maryland Science Center  for free.
Baltimore  was made famous by the movie Diner; the diner in which the film was shot is now the Hollywood Diner , off the beaten path near City Hall, but it’s worth a detour if you want to say you ate there (and ate cheaply). Two other bargain faves are Jimmy’s Restaurant  in Fell’s Point and Werner’s Restaurant , near the Inner Harbor.
And with all the money you saved, if you’re in town on a Tuesday, you should head to Gertrude’s  in the BMA for $10 Tuesdays. Any other day of the week, go to Hampden’s Angelo’s Pizza , and get a hot, delicious slice that’s the size of an airplane wing, and only about $3.
A “happy hour” can, at some places in Baltimore , last up to three hours, which is happy news indeed. There are plenty of great microbrews to try, but they’re pricey; order a “Natty Boh” (National Bohemian), and you’re probably looking at $2, tops, for a cold, perfectly adequate pilsner that’s a Charm City staple during hot summers.
Most Baltimore bars — bars, mind you, not clubs or lounges — are going to be relatively cheap; so are indie clubs like The Ottobar . Baltimore’s young, resurgent music scene plays at places like Metro Gallery  and Charm City Art Space .
People-watching is also a great, free option, and Baltimore’s got plenty of characters: pull up some stools at bars like Club Charles , The Brewer’s Art , and the Mount Royal Tavern  and enjoy the show.
Start by perusing one of the city’s free papers with good event listings: b, put out by the Baltimore Sun, is printed every weekday; while City Paper comes out weekly. Also check out Baltimore’s  visitor website, baltimore.org, for happenings and bargains.
During most of the year, you’ll find live music all over town on First Fridays, which takes place (obviously) on the first Friday of the month. Most museums and gathering places will have some sort of special events, bands, or entertainment, and many shopping districts stay open late.
Scholars, artists, and authors frequently give shows and performances across town at universities and libraries. For just $15, you can get a “best available” seat to see the acclaimed Baltimore Symphony Orchestra under conductor Marin Alsop.
Free outdoor movies have become a Baltimore tradition, and they’re available in several flavors: Little Italy’s well-attended summer series, Little Italy Open Air Film Festival (www.littleitalymd.com ), from July through August, shows (generally) tried-and-true Hollywood hits, all (generally) with an Italian or Baltimore theme or protagonist. At Federal Hill, the American Visionary Art Museum’s Flicks from the Hill (www.avam.org/cgi-bin/Events.cgi ) screens a broader range of Hollywood classics and more recent hits of the quirkier variety, projected on the side of the museum in June and July. And Johns Hopkins University, Johns Hopkins Summer Outdoor Films (www.jhu.edu/summer/films ), shows family-friendly films in June and July on its main quadrangle.
Take a hike through bucolic Robert E. Lee Park  and meet a lot of happy canines. During spring, you can have a day at the races at Pimlico Race Course , the home of the Preakness , for a paltry $3 — and you don’t even have to place a bet. Tuesday nights are $8 upper deck nights at Oriole Park at Camden Yards . And an old sport has gained fresh legs and a wicked forearm check — go see a Charm City Roller Girls  roller-derby match, where 10 bucks gets you two furious bouts.