The Ballachulish Horseshoe. Aviemore 91 'The tough turn back' off road epic. And what those ratings mean Rating Meaning Silly You might get hurt tripping over your own shoelace. Planning begins two days in advance. Serious Suffering, training and some planning.
Risks are mostly subjective.
Very Serious More planning, more objective dangers, such as avalanches. Extreme A serious logistical exercise with extreme hazards, including altitude, weather and terrain.