We enjoyed Ron's number puzzle so much (An Infuriating Puzzle) we looked for another and found another great one 
NotPron
This one is pretty famous and is billed as the Hardest Riddle on the Internet, but don't let that put you off - it's tough but so far doable with a bit of thought and there are clues on the site for the first 10 levels. A bit of everything - source code, url changing, codes, observation (put some of the pics, etc into graphics prog and alter to find hidden clues) logic - etc.
If you have a go let us know. And we could use some (hidden) help on Level 20 where we are currently very stuck! 
Well I have seen NotPron before... and gave up.... perhaps I will give it another go...
Merry, we are off to Hereford today...... so we will wave when in the queue at the top of Birdlip and you may see us
Oh do have another go Ron. I'm loving it!
I went to school in Birdlip, lived in a lonely little cottage at the top of Birdlip Hill (think a bypass goes round it now though) - on the road to the Highwayman Inn which used to have a stagecoach in the front garden... and I went to the village school there from the age of 6 - it was a nice little school. The only think I remember learning there was Maypole Dancing though It was a 3 mile walk to school, kids of today, don't know they're born..
Hereford is where Helen was born - this was unplanned of course as she was two months early and popped out all of a sudden on a day trip there 
So you are visiting lots of my old haunts today
This looks fun. I'm on # 4.
I'll let you know Merry how I get on.
Oh please do post your progress, Isis 
Glad you are enjoying it!
Well I shouldn't have spoken quite so soon. I breezed through 1-4 and now I've come to a screeching halt. 
Hints
if you are looking at 4: save the picture and lighten it quite a lot in a graphics prog. you may see something you couldn't before... and then perhaps need to Google to translate it
If you are looking at 5: you need to Google lyrics and artist for the answer to this level (two words) which go in the password box (red knob on remote control)
We are completely stuck on our level
I did figure out 5 in the end 
I'm on 6 now.
It would help to have someone else do it with me, so trying to con persuade a pal to do it too. 
well done Isis!
It actually says in the NotPron forum that it is nearly vital to have a partner or a group of you - certainly some of the levels I wouldn't have had a hope of solving without Pani.
We are on level 72 now. It's been a fantastic bit of fun and very satisfying, while infuriating at times. Very varied challenges and some of them incredibly intricate but all have been very logical once we got the answer.
The latest level involved cutting and sticking a shape together out of paper and a few more twists I won't give away - took us two days to crack it - phew.
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