The Mystery of Locked Rooms by Lindsay Currie

Crack the codes. Find the treasure. Escape the house. From the acclaimed author of Scritch Scratch and What Lives in the Woods comes a action-packed adventure novel about three friends who team up to find a hidden treasure in an abandoned 1950's funhouse. Twelve-year-old Sarah Greene wants nothing more from her seventh-grade year than to beat the hardest escape room left in her town with her best friends, West, and Hannah. But when a foreclosure notice shows up on Sarah's front door, everything changes. Since her father became ill two years ago, things have been bad, but not lose your house bad...until now.  Sarah feels helpless until the day Hannah mentions a treasure rumored to be hidden in the walls of an abandoned funhouse. According to legend, Hans, Stefan, and Karl Stein were orphaned at eight years old and lived with different families until they were able to reunite as adults. Their dream was to build the most epic funhouse in existence. They wanted their experience to be more than mirror mazes and optical illusions, so they not only created elaborate riddles and secret passages, but they also claimed to have hidden a treasure inside the funhouse.  Once in, Sarah, West, and Hannah realize the house is unlike any escape room they've attempted. There are challenges, yes, but they feel personal. Like the triplets knew who would get in. It seems impossible, but so does everything about the house. As soon as they're in she immediately worries that attempting the funhouse is a bad idea but Sarah has no choice but to continue, since her future is at stake.