You can easily take a taxi both ways. I'd guess the fare would be 12-15 dollars. Public transportation is also easy, but it's not the shortest route and will take some time - the F-line (above ground train) and that'll take you right to the castro. You could also take the 47 bus and the transfer at Van Ness and Market to the F or the underground. But... I'd just take a cab!

…511.org/static/…SF_7122007102343.pdf

F line, end to end

Both good suggestions. Take the F line there and catch a cab back.

Be careful on the F line in Fisherman's Wharf and along the Embarcadero where it is very crowded and fairly touristy. Pick pockets have been known to target this line. Wouldn't want to lose your drinking money :)

If you don't care about being above ground - you could take the F-line to Embarcadero station and then switch to the subway. Any K, L, or M train will get you to Castro Station (N and J lines split off before reaching Castro).

And if you get tired of the crowded or noisy bars on Castro, you can find respite at Eureka Lounge:

http://www.eurekarestaurant.com

Restaurant is downstairs, sedate bar is upstairs.