Halloween treasure Hunt for older kids (12+)

[ICantFindAFreeNickName]

We are having a Halloween party and my ds has helped set up an indoor treasure hunt for the younger children. He's now announced that I need to set up a treasure hunt for him & his friends and that they need harder more cryptic clues (wtf! - you'd think that after 12 years with me he'd know my limit is a couple of ryhming lines that even a 3 year year old could work out). However he has been very helpful, so I don't want to let him down.
There seems to be lots of treasure hunts online that you can buy, but can anyone reccomend one. I don't really want to spend £5 and find it's rubbish. Or even better has anyone found a free treasure hunt thats suitable for older children?

Bumping for the daytime crowd, can anyone gives me any ideas

Bumping as I also need to organise a treasure hunt.

If you tell us some hiding places I'm sure there are lots of clever people on here (ie not me) who could help you to write clues.

I'm not sure of any hiding places at the moment, just anywhere in the house (downstairs preferably).

Do you have any code books?

ds1 loves doing and organising treasure hunts, and usually writes the clues in codes. He then provides participants with a booklet explaining the different codes, and they need to work out which code the clue is using before deciphering it.

Any good?

Roisin, thanks for that idea, I will see if the kids have got any old puzzle books lying around. that I can copy a code from.
p.s Next time Im just going to borrow you son for a few days, it sounds like he is full of great ideas!

Some easy hints/tips from him:

You can do some simple codes with just one letter or number of symbol substituted for each letter. If you do it carefully you can convert the messages using find/replace in MS Word.

To make it more tricky don't put spaces in where the words end, but just split after each 5 letters.

To make it even more tricky you can then reverse each of these 5-letter-words.

Or you you can write the entirety of the message backwards (in code).

Either in code or not, you can write the message in on every 4th letter with the rest being just random gobbledigook.

Etc!