Make sure you have shut off everything in the Waterfall room before pushing the buttons at the Power Box. Click combinations until both symbols for the Waterfall are green. Then, go back and open the floodgate, and, watch your head.
Fireplace puzzle in the parents bedroom
There is an incomplete 'chessboard' in the fireplace-elevator, which takes you down to the two books. Number the fields on the incomplete 'chessboard', starting at the bottom far left corner, going left to right: 1 to 8. Then for the next row: 9 to 16, and continue the pattern with 48 in the top far right corner. Try pressing: 9-34-6-16-30-19-20.
Serenia
Serenia is the most incredible aspect of this game. Create a save point in Atrus' Library. You will want to visit and re-visit Serenia. Earth, Air, Fire and Water, and you will be a different Child if you keep going through. The best part is where you finally get into Dream. To Harmonize The Ancestors, ask yourself where do all colors begin ?
Tomahna: Bug Cage
While in Tomahna at the beginning of the game, do not open the glass cage containing the bugs unless you want Yeesha to get angry with you for ruining her experiment.