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. :)
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.