When my son was 8, he loved ROCKS. I did a geology adventure, with an archaeology treasure hunt. I dressed up as the tour guide with hat, rope, cargo shorts, etcetera. I bought a gift bag of different rock samples including a fossil, a geode, a quartz, and other interesting rocks.  There was a sheet explaining the rocks in the gift bag. This was the goodie bag" to take home." Then I started out with a "treasure map" which I had made on parchment paper and burned the edges with a match to make it look really old. We went into the garage it was dark.  We lit a candle and I had a fake skull and we talked about the adventure ahead.  We went through a "tunnel" that was made out of cardboard refrigerator boxes and decorated to look like a cave. The kids all crawled through the cave to go on their treasure hunting geology adventure. They used the map to find the first clue.  Each clue directed the children to a new place in our yard and had some information about "ROCKS" so the boys really were interested in the clues. One clue was "climbing the mountain" which was actually climbing over the swing set.  One clue was "the rope bridge over the snake pit" which was actually climbing up the steps to the deck. (ropes on the railing some fake snakes)  Of course the clues need to fit what you have in the house or yard.  I included some rock facts. The last clue was on our deck.  You had to look down then there was a large "X" in the old flower bed.  They had to dig at the "X" to locate a chest. It was filled with fake gold coins and "treasure" which was candy (shaped like rocks and rock shaped bouncy balls and rock sugar geology related items).  Then we went inside for the pizza and cake.  The cake was made to look like a geode.  It was a firm cake (I used 2 pound cakes put together and rounded off at the edges) hollowed out and there was rock candy in the hollow part to look like the crystal in the geode. The frosting was grey to look like the outside of a rock. There was some shattered rock candy around and a small hammer on the tray so the whole cake looked like a broken open geode. The kids (it was a boy party) were so interested in the whole rock and treasure theme."