i went on a great hen night to brighton recently. we went for a pole dancing lesson! it was great fun (after we all got over our initial embarrassment) and surprised ourselves and each other with our moves! this was booked through a company called chilisauce:
http://www.chillisauce.co.uk/ and was good value.
i've also been to cork for a great hen weekend a while ago (there were 30 of us!) and we went quad biking and also went to blarney castle to kiss the blarney stone. a good weekend.
on both occasions we did a mr & mrs quiz. this is really good fun - you basically get a load of questions which you ask the groom and on the hen night the bride must try and guess what answers the grrom gave. for every wrong answer the bride must do a dare or a challenge (things like 'must kiss a bald man on his shiny head').
good luck!