Complex sentence: In very poor weather Bonington's expedition failed to reach the summit but the team gained a great deal of experience, in particular discovering that the line above Camp 6 was not as favourable as they had anticipated.
Split into simpler sentences: In very poor weather the expedition failed to reach the summit but the team gained a great deal of experience. In particular, they learned that the line above Camp 6 turned out not to be as favourable as they had anticipated.