There are more possible combinations in a 6x6x6 than atoms in the universe! Nevetheless, the best speedcubers can solve it in around 80 seconds on average. Solving it is similar to the 4x4x4 and 5x5x5 but a few extra algorithms known as commutators are useful for solving centres. 6x6x6s are probably the most complicated WCA puzzles to design but despite this, there are many excellent options available.