70 degrees is a temperature that is a given ideal maximum. It can fluctuate but you dont want it going to high above 70 degrees due to fears of beetle hatching. Too low a temperature, and you could have trouble maintaining a certain level of humidity (I do during winter sometimes). What is most important is the humidity, as its the humidity that keeps the cigars from drying out which makes them burn hot and taste harsh.
I keep my humidor in the coolest room in the house out of the way of direct sunlight and it seems to do fine. If you have serious problems keeping the humidor temperature down and if the humidor isnt an ornamental thing for you, then you can always stick it in a picnic cool box.
Make sure you season the humidor for at least a few days to stabalise the humidity in the humidor first before you use it. If you dont then when you put your cigars in they will drag your humidity level right down and it will be too dry in there.