Here is a challenge. Place queens on a chess board such that no queen can take another in one move.
The queens are indicated by yellow squares, which can be clicked to place and again to be removed. Squares which are blocked by placed queens are represented by red. There is definitely a solution of eight queens, but are there more? (Not counting mirroring and rotations)
This challenge was first presented by Max Bezzel in 1848. It took two years to be publically solved, and yet with the tool above people can find a solution in minutes. I think this speaks to the power of the human brain when it is given a tool to quickly iterate over a problem.
For comparison, this is a computer's attempt to find all solutions. Built to present a straightforward algorithm visually rather than for speed.