Defending Your Castle: Build Catapults, Crossbows, Moats, Bulletproof Shields, and More Defensive Devices to Fend Off the Invading Hordes

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Gift: a built-it yourself functional catapult, trebuchet, etc. from Medieval Kits (search - it was a Kickstarter, now a dot com)
bonus accompanying book: Castle, by David MacAulay (but geared towards more of a juvenile audience, like teens)

Even if you don't have a house of your own... or perhaps ESPECIALLY if you don't have a house of your own and have to put up with obnoxious neighbours 'all up in your kitchen' as the saying goes, this book makes glorious fantasy reading (entertaining and educational, too!). And the kits from Medieval Kits are so good that we have two (and will probably acquire more. I should have bought another for this year - kept him busy all Boxing Day!)