There's nothing special about cycling. You can deplete your glycogen stores and hit the wall with any aerobic activity. If you have a healthy metabolism and stay in heart rate zones 1-2 then you'll mostly burn fat stores and can cycle for many hours without hitting the wall. At higher zone 3+ efforts you'll need periodic carbohydrate supplements to keep going.

Indeed, but you can keep going just about. I've properly hit the wall once, and that was an unpleasant experience - nearly fainting and seriously in danger of falling off my bike, but I think that was largely a hard removal of all accessible glycogen, and it was years ago when I was relatively green. Now I just tend to eventually find it hard and unpleasant.