Calling All Breadmakers

I've been on a breadmaking kick lately. I had beginner's luck with my first loaf (maybe had something to do with using rapid-rise yeast, too), but since then I've encountered some difficulties: my loaves get these huge caves in the middle, as you can see from the pictures of today's loaf. (Actually, the all-bran loaves that I tried last week had even bigger caves in them - big enough for Tom, Becky, and Injun Joe to hide in, it seems.) You can see that the dough in the bottom of the cave is somewhat underbaked, but the outside of the loaf looks lovely and tastes fine.





I'm wondering if the cave is a result of overproofing - from what I've been able to read on the internet and elsewhere, it appears that that could be the case, but I'm not entirely sure. At first I thought it might be due to underkneading, so today I tried to remedy that.



Anybody have any ideas/tips/hints?

I wish I had learned this from my mom and/or grandma - no doubt they would have been able to tell me where I'm going astray. (There's something to be said for apprenticeships.) My grandmother was baking the family bread by the time she was eight - and here I am, trying to produce a decent, edible loaf of bread. Well, I more or less have the edible part down, I guess....