Yeah in many of the large houses here which were exclusive in the 1900's but now open to the public you can often see the ice houses where its like an underground bunker which was full of ice. Once the ground gets down to a certain temperature it apparently holds that temperature almost indefinitely. So you could get ice all year around. Apparently, if you add salt to slush it goes to about -10degC so you can use some of that to cool other ice and thats what causes the salted ice to melt even though its below zero temperature. But eventually you have to throw the salted ice out and start again.