A full bookshelf not only provides a conversation piece for guests, but also lessens the odds they'll pull out the tome that triggers the trapdoor to your shrine to Don Knotts. Build up book collections and safeguard secrets with today's Groupon: for $20, you get $40 worth of used, rare, and out-of-print tomes at Cupboard Maker Books in Enola.

Within its page-filled premises, Cupboard Maker Books stocks more than 100,000 hard-to-find hardback and paperback titles in categories ranging from Americana to writing. Foxtrot into an unusual collection of miscellany by F. Scott Fitzgerald ($6.11), ideal for Jazz Age aficionados or lovers of dignified first initials. Mystery lovers thrill to Arthur Conan Doyle’s classic Memoirs of Sherlock Holmes ($1.99), and fans of visual art and brevity may curl up with the 61-page illustrated version of 20,000 Leagues Under the Sea ($3.87) in the store’s comfortable lounging area. Should stacks of selections cause seekers' heads to spin, a staff of friendly bookworms is always on hand to offer recommendations or help find specific titles with expertly wielded dowsing rods.