Picked up the girl I am currently dating by going to a bar alone (I just moved to a new city and do not know many pepople). I basically went in, ordered some food and drinks and made small talk. I wouldn't recommend targeting bartenders as they get hit on ridiculously, but if you are cool and relatively good looking, they may pursue you (this one offered me her number without me asking).
Previous to this I did go to bars alone quite a bit as I travel for work a lot. While I wasn't going specifically to pick up women, it is always on the back of my mind. Generally speaking, it is a low percentage game but I did occasionally bring women back to my hotel room. 95% of the time I just sat there and ate/drank and watched sports.
Honestly, alot of it is going to come down to hour attractive you are and how personable you are. Unless you say you are traveling for work, their first thought is going to be that there is something wrong with you. You need to correct that fast if you are going to have any luck. I used to go to a bar in my previous city by myself because I had a couple friends that bartended there. I was mostly going to hang out with them and essentially drink for free. Pretty much every girl I would talk to would ask "why are you here by yourself?" Once I explained I was friends with the bartenders it was acceptable, but if you don't have a good answer you will probably be percieved as weird.
Really, you are better off finding some friends (1 or 2) to go with, preferably with the same agenda as yourself.