The environment is less scary than I thought. What I found creepy were a dirty plastic doll and a bath tub filled with blood.
Tools, keys, and gems are easy to spot. Puzzles are well linked to their clues. Therefore, I had no problem finding 10 beautiful stones.
Having discovered some symbols on brown bottles, I knew I had missed a puzzle box, but I couldn't find it even after searching all the rooms again. Thanks to the walk through, the puzzle box was located at location Q. And I pried a loose wooden board at location R and received the last blue stone.