Stupas at sunset, Bagan, Myanmar
As a general rule, a stupa is a solid structure that typically cannot be entered. They were constructed to contain sacred Buddhist relics that are hidden from view in containers buried at their core or in the walls. Temples. by contrast have open interiors that may be entered, and in which are displayed images (usually one in smaller temples, four or even eight in larger double storied temples) of Buddha as a focus for worship.
For an example of a large temple, see Dhammayangyi Temple and read the story of the psychotic King Narathu here http://goo.gl/7RzK2