I always thought Luke guided himself into that shaft on the sidewall thing. I guess as a kid it didn’t occur to me that he was possibly choosing suicide over joining Vader and that he planned to fall into the shaft to escape. I thought if he continued to fall he would have just hit solid ground at some point. I never really understood exactly what purpose the tunnel served and as a kid found the whole sequence to be kind of weird, but apparently everyone here is an expert on the inner workings of Cloud City.