Michael Dahl 
Seven Doors to Death [PDF ebook] 

As Zak Nine and his friend Erro make their way around a strange lake, they discover an ancient golden building. The boys decide to go inside to take a closer look, but unwittingly stumble into the legendary Octagon: an underground chamber with eight mysterious doors. One door will lead the boys to freedom, but the rest lead to sinister traps and certain death! Will Zak and Erro outwit the deadly room and escape before it’s too late?