Minecraft wiki entry for Exploring_caves, associated text: To reach ores or tunnels high on the ceiling, try pillar jumping to gain altitude or use Ladders by placing new ones as the player climb. Players can also build bridges across ravines and pits. Scaffolding can also be used for this.
If the player sees a huge underground ravine and wants to see what's inside of it, and they want a way to get back up but don't want to take the time to mine or place blocks, pour water on the edge and it will flow down, allowing for a safe way to get down and up. Note that players must have a water bucket with them, or if they have an empty bucket with them, they will likely be able to find a water source to get water from.