Our compost pile! What is this?

We throw just about everything into our compost pile, regardless of what you are “supposed” to put in it.  We put leaves, grass clipping, weeds, wood stove ash and the occasional kitchen scraps.  Our compost pile has been more a place to put the discarded vegetation than any attempt to create the perfect soil.  Last year, Kevin moved the pile to a different part of the yard, next to the vegetable garden.  Once every few years we actually use the new soil to fill in a new bed or hole.  Occasionally we notice some weeds growing in it and Kevin runs the rototiller through it a couple of times a year.  But then this thing starting growing.

What is it?

And then we went on vacation and it got HUGE!  It appears to be some kind of gourd, but no flowers or fruit yet! Anybody know what it is?

I am thinking either cantaloupe or watermelon.  Maybe summer squash or zucchini, but the leaves don’t look quite right for those, too rounded. I can’t imagine that it would be pumpkin. We have tried and tried to grow pumpkin to no avail!