"Believe me, my young friend, there is nothing - absolutely nothing - half so much worth doing as simply messing about in boats.”
Here are three classic River Puzzles, which require you to get a group of people, things and whatnot from one side of a river to the other, by sending a rowing boat back and forth several times. There are lots of these about, but the three presented here are good examples of the genre.
0:30 - Puzzle 1 is the classic farmer, fox, hen and grain. The farmer needs to get across to market, hopefully with all of his goods intact on the other side.
1:25 - Puzzle 2 has three pairs of monsters needing to cross for inexplicable reasons. The adults, despite their apparent friendship, can't control their monster instincts, and will eat each other's child monsters if given the opportunity.
2:34 - Puzzle 3 has 4 familiar gentlemen attempting to get across as fast as possible. But two of them don't appear to be trying particularly hard.
Here's a PDF you can download, cut out and use to try to solve each puzzle. The artwork came from various sources across in the internet. The Mr Men are from Roger Hargreaves timeless tales. I forget where the others came from.
The solutions follow, but you really owe it to yourself to attempt to solve them - none of them is particularly difficult. Logic and determination should be all you need.