Kids' activity book about a little boy and sister in search for the legend of the giant turtle

Hi, I used to have this book when I was much younger (~1997) about a boy and his sister (I think Aztecan) who set off in search of a legendary giant turtle.

It is more or less an activity book which had a tablet-like-bookmark (made of card, of course, with dimensions roughly ~10x10 cm). The corners of this tablet-like-bookmark had bees on them, and about 5 holes to see through. Throughout the book there were hidden things we had to find by placing the tablet on each page, aligning the bees on the tablet to various coloured bees on the pages. The correct orientation of the tablet would reveal these hidden objects.

Usually each double page had 3 things we had to find:
1) Our next destination.
2) How to get there (either by road, river, bridge, etc.).
3) A small activity regarding that particular page.

The book was not very long, about 30 pages or so but, it was very coulourfull. Enough to hide all the objects and markings. A few pages I can remember are: The Ravine, where a monster is in the ravine which you need to cross by walking on one of the two wooden bridges. One of the bridges has maggots in them and will break. So this is where you use the tablet, with the help of the bees, to know which bridge is safe to cross. Other pages include The Observatory, The Waterfall. Unfortunately I really can not remember the rest.

This book was targeted at ages 5~9 (I guess). I would really appreciate it if anyone knew it. It was so much fun at the time, just wish to get my hands on it again and preserve it!

The title sounds something like:
Legend of the Giant Turtle or
Search for the Giant Turtle or
The Giant Turtle of ...

Is it Turtle Quest by Piers Harper?

WOW YOU ARE THE BEST!!!!
I truly cannot tell you how grateful I am...
Seriously, you made my day... I have been searching all over the web for it... Trying every iteration I could think of as a name!
Again, thank you ever so much!

There is just one other book I've been trying to find... It would be amazing if you knew that one too... Let me give a brief description:

This book was paperback, black and white, was targeted at ages 10~15 (again, I'm guessing) and I remember reading it around 2002 (give or take a year)...

It was about seeking a mysterious ghost haunting a mansion/castle (I cannot remember) where a deceased family lived... You start of at page one and have to solve each of the riddles/problems... You could end up with various answers, and depending on your answer, you are instructed to go to the respective page (to advance in the storyline, you need not read the pages in sequence)... For example you may be on a page with 3 gates drawn... Only after solving the riddle correctly will you know which the correct gate is (and hence the appropriate page number to turn to), in order to advance the story-line... The other gates may lead to dead-ends, death, etc...

The book was filled with pictures (black and white), sometimes the riddles were picture related, and sometimes they were only text... All I can remember is that the ghost was an old lady (I think the family's grandmother). I don't exactly remember where she was hiding, but it was definitely either the catacombs or the place where plants were kept (not sure if the book called it a nursery)... But there was a trick to be able to see the ghost... You had to tilt the book almost horizontal to be able to see the old lady!

I hope you get the main gist of the book...

Once again, thank you for helping me find Turtle Quest

You're more likely to get helpful responses if you start a new thread dedicated to your second book request, Daimason!

I guess you are right. Just wanted to see if Osunale knew the book I was talking about.

Yeah. But more people will look at it if it's in its own thread (with a good title, like this one), so you've got a better chance.