Rock-climbing is good. However, I have found that if you lack a baseline of fitness, you won't get a whole lot out of it in terms of pleasure- at least for bouldering. For example, recently I bouldered for a month or two, and reached a point where I could do easy tracks with relative ease, but medium-difficulty tracks were for all intents and purposes impossible. My right arm and my pinch grip were simply not up to snuff, and when they aren't good enough to use on the rock I can't develop them through use!

Anecdotally, it seems like a great sport to hone and maintain your physiquie, and perhaps motivate you to develop it, but it does not seem to stand alone well for developing.

(I'm in decent shape; some examples of the holds that stopped me cold were hanging on an inverted face from pinch grips, and tricky holds where the face is again steeply inverted, your hand is by your waist, and you pull your chest up against the rock with that hand. Just not even slightly within my abilities)