It's easy to find a bar in Key West. On Duval Street alone you could start at one end, the Sunset Pier at the Ocean Key Resort at 0 Duval Street, and work your way to the other end, The Southernmost Beach Cafe and Bar at 1405 Duval Street. In between you can find world famous bars, Sloppy Joe's at 201 Duval, Margeritaville at 500 Duval, and just off Duval, Captain Tony's Saloon at 428 Greene Street. Within just a few blocks you would pass the Hog's Breath Saloon, Ricks, Dirty Harry's. There is, seemingly, no end.
But there are also a number of smaller, local bars that are off the beaten track. One is actually on the beaten track but if you blink you might miss it. Here are some examples.
The Bottle Cap Lounge and Liquor Store, 1128 Simonton Street. If you visit the Southernmost Point at the end of Whitehead, walk back across Duval to Simonton and the Bottlecap Lounge. Store hours: Noon - 4:00 a.m. Lounge hours: noon to 4:00 a.m. DJ's and Videos: 11:00 p.m. - 4:00 a.m. They even advertise "Off The Beaten Path," and they're not kidding.
B.O's Fishwagon, 801 Caroline Street. This is not off the beaten track nor is it known as a bar, but you can walk by B.O.'s every day and think that it is under construction or condemned. Stop in for a Conora and a basket of fries, sit on a stool at the railing, and watch other people unknowingly pass it by.
Charlie's Place, 908 Kennedy Drive # B
The Chartroom at the Pier House, 1 Duval Street. You could wander around Key West and even the grounds of the Pier House and not notice this bar. You might even stay at the Pier House and miss it. But it's there, with peanuts on the bar, a popcorn maker, and free knockwurst sandwiches. Rumor has it that Jimmy Buffet got his start here, Jim Croce performed here, and Tennessee Williams passed out here. It's best when there is a sporting event on the TV.

Dante's at 951 Caroline Street. If you walk along one side of the Historic Walk at the Key West Bight you will pass the Schooner Wharf Bar, Turtle Kraals, and usually stop when you get to the Half Shell Raw Bar. But going a little farther will bring you to Dante's. As with the other bars at the Bight they feature a happy hour (Mon-Fri 4pm-8pm) and Specials (Everday 4pm-8pm; Oysters, Clams, Shrimp and Florida Stone Crab Claws) But bring your bathing suit here. As long as you order something to eat or drink you can use their pool.    
Gumbo's Boat House, 1445 South Roosevelt Boulevard. This is so far off the beaten track that you will need a car or a bicycle to get there. One happy customer enthused "GUMBO's bar was very relaxing, hidden and tons of fun!! DEE, MELINDA , MARCY, MIKE and JIM made everyone all feel at home and very welcome!! Although they only serve beer/wine it was a fun, personable crew to hang with on the trip, everyone enjoyed themelves very much and plan to go back. Nice to get out of the hustle and bustle of Duval Street!"
The Live Bait Lounge at Key West Bait and Tackle, 241 Margaret Street. Their web page says it all; "Come in and join some of the local Key West characters for Happy Hour and share a few stories of the big fish that got away. There is plenty to look at from the patio of the Live Bait Lounge or come inside and watch the game on a big screen TV and look at some of the old Key West decor that adorns the walls of the shop. If your wife drives you to drink...have her drop you off here!"
Mathieson's 4th of July Ice Cream Restaurant, 1110 White Street. Even non- drinkers can find an (ice cream) bar off the beaten path. As one visited said, "This restaurant was a favorite in Key West! What a fun atmosphere! You can enjoy the old soda fountain nostalgia. Even though there were people  in their 30's it was so nice to enjoy a place like that one's parents enjoyed. The food was delicious, service friendly, and the desserts simply heavenly! A favorite was their "Smores Sundae". 
Bobby's Monkey Bar, 900 Simonton Street. Bobby's is one of Key West's many Gay bars and features a Happy Hour from Noon to 7:00 p.m., Karaoke on Sunday nights, pool tournaments on Tuesday nights at 7:00 p.m., and provides internet access. 
Pepe's, 806 Caroline Street. This is known primarily as a very good local restaurant, but many of the locals enjoy a drink at the small bar in the outdoor dining area. There are $2.00 bottles of beer and free bar food is passed around among the people at the bar and others waiting for dinner. Seating is very limited at Pepe's bar. 
The Smallest Bar in Key West, 124 Duval Street. This bar is on the beaten path but you could walk up and down Duval Street every night and miss it. It's surprising it has a full street address, it might hold a half dozen, small  people, and is probably the only BYO stool bar in Key West.  
The Tiki Bar and Deli at the Galleon Resort, 617 Front Street. When people walk to the northern end of Simonton they usually turn right to the Historic Walk and the Key West Bight. But if you make a left you will find the Tiki Bar and Deli at the galleon Resort. The Tiki Bar is another good place to have a drink and watch the sunset, one that few know about or will wander into.  

The White Tarpon Bar and Liquor Store, 700 Front Street. The street address might fool you into thinking the White Tarpon is on a street. It isn't. It's tucked under an overhang at the Key West Bight between Alonzo's Oyster Bar and the Commodor. In the afternoon there is generally a barrel filled with ice and $2.00 bottles of beer, but the buzz here is the variety of martinis; chocolate, Key Lime. etc.