We spent two nights in Kalmar, huddled in pubs as the wind off the Baltic whipped through town. The leaves had just begun to change. Our room was almost in the shadow of the castle's copper roofs, the moat was just outside our door. We explored the castle from top to bottom, poking into places we weren't supposed to and walking around the marshy perimeter.
The castle's rooms are mostly used as exhibition spaces these days. History (old robes, plundered furniture, building models) was superseded by a vast collection of Bjorn Borg photographs (why?) and a room of paper cutouts. Painted, paneled and restored ceilings are the architectural highpoint. Electric fires radiate weak flickers over every hearth.
Cannons swiftly changed everything about military architecture (I've talked about this in Castello di Trani, Kyrenia Castle, Palamidi Fortress and soaring Kotor ). In terms of shore defenses, it changed things even more. Before the advent of gunpowder, all that was needed to defend a port was a garrison of men - ships could only feebly attack land from the water and the real fighting was done once the attackers had come ashore. After cannon were invented, ships and castles became direct adversaries.
The high old battlements were too delicate for the new cudgeling, so the outer walls of Kalmar, which rise directly from the water, are thick, low and earthen. They didn't need to be very high, because attacking gun batteries would be firing on a horizontal plane. Along the top, cannon ramps were installed for moving large guns, and firing stations were established. Massive bastions were built at the corners, and a gatehouse was positioned at the back, fronting a wide moat. In essence, the old castle was given a protective booting of sod and stone, and so was freed up to be made more luxurious.
As the new border between the countries was moved southward in a complicated treaty, Kalmar lost a lot of its strategic significance. It continued for a while as a secondary royal residence, but eventually fell into disrepair. Before it was spruced up in the 19th century - as a curio - it was reportedly in very bad shape.
Make no mistake, even in the 1500's, there were plenty of monarchs and low gentry who romanticized the middle ages, even as recent as they were. They were rapidly taking disused piles and turning them into whimsical, fashionable country homes. Most "renaissance castles" were built or renovated for show. At Kalmar, under threat of imminent attack, the King built a true limestone stronghold, then made it livable. By the cold, dark waters of the Baltic, Sweden has a special treat - a place where function and fancy have been given equal billing.
(And, if you can sneak in, the attics are one of the great castle experiences of Europe!)