I did the Grim Challenge in Alderhot December last year
http://www.grimchallenge.co.uk/And the "Rock Solid Race" in March this year near Exeter.
http://www.rocksolidrace.com/Grim was minus 2 when we started and the ice was an inch thick on the puddles, no real obstacles in it just Mud and puddles, but was quite challenging as it was on the M.O.D vehicle testing grounds.
Rock Solid was just that, with all the obstacles.
Do IT!!!!! You'll love every bit, but the only thing is it is HIGHLY ADDICTIVE. Can't wait til the next one, only a small 10k in september before a 5k in october then the Great South Run at the end of october then Grim again!!!

And I hated cross country at school.