@gollum,
My tried-and-true method was epsom salt soaks...2x per day - early in the day and just before bedtime. These salts draw out the toxins (lactic acid) from your body.
I'd advise drinking lots of water to flush your body of lactic acid...even now.
For the future in order to avoid that sort of pain it's advisable to train a bit before attempting such a feat. A month or so of running 3 - 4x per week of similar distance could be adequate.