Madeira is a famous wine made on the island of the same name, a possession of Portugal. It figured in early American history, as an off-shoot of the significance it had in the British world. It comes in different degrees of sweetness, but the sweeter types are generally the better known. Malmsey is an example.
It is reputed for never going bad, in that, part of its production involves exposure to extreme heat, either in warehouses or barrels being rolled in the sun or both. (Particulars are easy to find on Wikipedia and similar sources). This derived from experience gained on ships: when Madeira was exported to hot climates, it was noticed it came into perfection, so later they emulated these techniques in a warehouse or other static environment to produce the same taste.
Mareira is a fortified wine (like sherry and port), that is, brandy is added to stiffen and help preserve it. Still, it doesn't exceed 20% ABV generally.
I can attest to its remarkable powers of preservation. About 10 years ago, I blended a 3 year old Madeira with a 15 year old of a different make. Since then, the bottle, now only 1/3rd full, has been moved around countless times, sits part of each day in the sun in an exposed bar (rattan-type two-level affair), gathers dust and is otherwise treated in a heedless fashion.
And yet, this blending tastes fresh as the new-born day. It has a slightly smoky, raisin-like palate, and is either as good as the day I blended it, or better. Yet, it has never been pasteurized or dosed with chemicals, never seen the inside of a fridge. I once read that, being exposed numerous extreme elements in its gestation stage, you can't hurt Madeira, all the bad things that can possibly happen have already occurred! Only spirits such as whiskey can resist time so effectively, and even that will succumb, ultimately. Madeira never will, it lasts forever or practically so. No wonder it was admired by pre-1800's connoisseurs.
It is still made, and while old vintages are around that cost a fortune, you needn't spend so much. Buy a 5 or 10 year old bottle, and enjoy a taste of history. Due to its natural oxidative properties and balance of sweet and acid, you can pretty much do your will to it, and it will respond by only being better.