@shadami
Gone-Away Lake
Excerpts from summary:
Julian and Portia pack a picnic lunch and set out to explore the woods. They find a giant boulder with Latin words inscribed on it. Julian translates two of the words as Philosopher's Stone and excitedly explains that such a stone was believed to turn things into gold.
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They come across a swamp with a rowboat in it. Before they can figure out the mystery of who would try and boat in a place with no lake, they see a deserted row of houses. Afraid they may have stumbled on a ghost town, Portia begs to leave, but Julian calms her long enough to hear a voice from a television. They search a little longer and meet Minnehaha Cheever and her brother, Pindar Payton.
Its sequel is "Return to Gone-Away".
I haven't read either book in this series, but I found it through some googling. :D
EDIT: Glad I could help! And lol, my google-fu still has a long way to go too!