Tunnel of Secrets (Hardy Boys Adventures Series #10)

When Frank and Joe set out to explore caves and tunnels, they dig themselves into some dark and dangerous trouble in this Hardy Boys adventure.

When a sinkhole opens up and swallows one of Bayport’s historic statues, Frank and Joe suspect something—or someone—shady at play. They jump at the chance to investigate; Joe as a member of an urban exploration club, and Frank as photographer for the school paper.

But in the thick of their search, the boys stumble upon an entire underground city that...