I don’t have any pictures of this one, because I have never actually had this problem. This isn’t because I’m some genius baker, but it is because I’ve been very lucky. Cakes fall for a multitude of reasons, but I think the most common one is rain/humidity. You’re home on a rainy day with nothing else to do, and you want something sweet so it makes sense to just whip up a cake. This is not a good idea. Baking is a science and everything has to be exact to the recipe your using when it comes to main ingredients, temperature, humidity, altitude, and barometric pressure. You can account for any of these changes. Also, a fallen cake isn’t necessarily a bad cake. It just won’t look as pretty. And don’t worry this happens to even the most famous of professional bakers sometimes.
Temperature is one of the largest factors in why a cake might fall. You have to cook a cake at the perfect temperature. You could have issues with this from something as simple as not letting the oven preheat fully before you started to bake, or using a different kind of oven. Note that most of the older recipes are made for electric and not gas so there will be a variation in temperature control and most likely cook time. Always check on your cake but try not to open the door to the oven too often.
Humidity changes everything. When it’s so wet that you’re sweating or it’s raining you’ll probably have to adjust some ingredients and cook time. Weighing your ingredients is something that should be done. The secret though is that 1lb of flour will weighed on a humid day will contain less flour. You’ll also notice a change in the weight of 1tsp of salt on a humid day. You’ll just have to play around with these weights in your own home on dry and humid days in order to determine what would be the amount needed.
Finally, you do NOT want to overbeat your cake. If you do this, you are a likely to have a fallen cake. It’s not always easy to know when you first start baking what its overbeaten, but we all have to learn from trial and error. The other thing I will say is that underbeaten cakes will also fall so you have to get it just so.
I know all of this makes baking a cake sound difficult, but it is not. You will learn to adjust for things here and there as the weather calls for it.