This is an ever-growing list of sites that can help you to understand and explore the mathematical world. If you have any suggestions for sites you think should be included, please don’t hesitate to mention them in the comments section and I will check them out.
Murderous Maths (see the Books section for the corresponding book series) – http://www.murderousmaths.co.uk
Brilliant (an online maths community for sharing problems, explorations and examples) https://brilliant.org
Sixth form level worksheets – http://www.bmlc.ca/PureMath30.html
Fractals – http://math.rice.edu/~lanius/frac/jurra.html
Cut The Knot – http://www.cut-the-knot.org
Math and the art of M.C. Escher (everything you could possibly want to know about symmetry) – http://euler.slu.edu/escher/index.php/Math_and_the_Art_of_M._C._Escher