I really like the puzzles on this site and they are all free.
If you want some stimulation I suggest you try some out.
Some are familiar and maybe not so hard. Others are very difficult.
Here are some number ones that I like. They are on the more difficult side but any bright 15-year-old could tackle them.
You only need basic maths skills and a calculator at the ready (along with a pen and paper)
Here is an easier set that you may find quite challenging still, they are set at different levels of difficulty.
There are a lot of logic ones too that do not involve any maths.
Put this in sticky topics!
Thanks for sharing this list, appreciate it!
It is already in sticky Topics under
@ Site full of printable puzzles.
Maybe I will swap it for this one. :)
If you are able to still edit the page you should definitely add this to it, but not remove anything.
Sporcle is another site that many of you would enjoy.
It is a huge site with all kinds of things you can play with and learn.
I think you can write your own games too if you have some programming skills.
But among its many attractions it has some really good logic puzzles.
I have not played with them for ages but I think they are mostly here.