“An adventure is defined as an exciting or unusual experience; it may also be a bold, usually risky undertaking, with an uncertain outcome.“
Not very satisfactory for me its lacking something about pioneering or isolation. Adventure isn’t just about risk taking nor novelty. Anyway.
With the world mapped and well enough trod there is no new, only new to you. Which should be enough for most people. I link bouldering and exploring/searching for new boulders unextractably. The physical side of it holds less for me but I do get it. Walking around wondering what around the corner, hidden in the hollow or over the ridge is exciting. Usually turns into disappointment but that’s just the way it is.
I suppose adventure is wandering around outdoors and whether you have a pad or rope or kayak on your back is secondary. So if you don’t think there is any adventure in bouldering you are just doing it wrong.