We've already done some multi-day canoe camping trips on the rivers. I'm not sure that has enough risk/danger for us. The first river trip I took him on when he was seven, I was pretty scared because the normally flat river was flooded and really flowing - fast and some small white water and waves. I was scared I would lose my son but he was in bow busting waves, getting wet, having the ride of his life and loving every minute of it. You should have seen the look of satisfaction and achievement on his face when we finished that trip! Sadly, he's not much into paddling any more. It's too much like work.

Same thing for hiking/backpacking. We've done a lot of it, including some trips that have been physically challenging. But he mostly sees this as something his Dad drags him along and makes him do. I'm trying to find something that will give him a thrill.
He's into guitars and is an exceptionally good player for only being 14. I really enjoy hearing him play. I don't know how I could build a manhood initiation adventure around that interest, though. Unlike his little brother, this son seems to have a negative attitude about everything. Not that he's a bad kid - he just never finds enjoyment or pleasure in anything. Even things I can visibly see he enjoyed - six weeks later he'll tell me how awful he remembers it being.
Scuba diving sounds like a real possibility. It could be a little scary and definitely has an element of danger. It requires preparation and training. It could involve a road-trip to Florida. His grandfather has done a lot scuba diving, too, so that is something we could share in common with him.
Spelunking is not a bad idea, either. Also requires some training - also an element of risk and conquering your fears.
A race car adventure might be possible - that's definitely up MY alley. But it could be humiliating for him to get smoked so badly by his old man in a racecar! It's impossible for me to go easy on anyone once I get a crash helmet on.
Thanks and keep the ideas coming boys!
Before qualifying for the initiation adventure, he will need to complete a physical challenge, a spiritual challenge, and an intellectual challenge. Each of those is something we will do together. Ultimately, I want the initiation adventure trip to be something he buys into. I want to come up with some challenging options and see what grabs him.