Many modern hotels in the USA provide in-room coffee service. Sadly, both the material and the equipment provided tend to be subpar, and can result in bitter-tasting coffee, which is made worse by the only on-hand buffering agent, nasty chalky dried creamer. Here’s how to make a decent batch of cold-brewed coffee, right there in your room:
Locate your coffee pot and a tumbler—a wax-paper soft-drink cup will work in a pinch—that fits inside when turned upside-down.
Carefully unwrap (don't tear!) one or two of those premeasured filter-packs that came with your coffee service and stuff it gently into the cup. Ideally you want four parts water to one part coffee, but this is tough to estimate with filter packs.
Fill the remaining space in the cup all the way up with water. Tap water works; filtered or bottled is better. Try not to leave any air bubbles.
Don't worry if it seems it will result in a tiny amount of coffee; it will be concentrated, intensely flavored, and—assuming you're not stuck with decaf—highly caffeinated.
Invert the coffee pot over the top of the very full cup, lower it until the rim of the cup seals firmly against the inside of the bottom of the pot, and carefully flip the whole assemblage over.
Under Earth-normal conditions, the twin phenomena of surface tension and atmospheric pressure will keep the water in the cup, the coffee packs will float to the surface, and there will be very few air bubbles.If you’re feeling nervous about this step, practice it over the bathtub without the filter pack.
Place the entire assemblage into your room’s refrigerator before you go to sleep. (Alert reader @chanelwheeler notes that you don’t actually need refrigeration to make cold-brewed coffee; yes, this will all work fine on a countertop at room temperature. I like my cold-brewed coffee to actually be cold, so I put it in the fridge.)
In the morning, pull the cup straight up, allowing the contents to spill out. Fish out the filter-pack and enjoy lovely cold-brewed coffee!
Note: your pot will only be about a third full. If you want the hot stuff, carefully guess the amount of water you'd need to fill the pot—you might want to do this the night before in your practice-over-the-bathtub stage if you’re feeling nervous—and fire it through the coffee maker directly into your cold brew. (Alert reader @chuckisthinking points out that if one tumbler fills the pot one-third of the way, you need two more to go all the way up. Thanks, Chuck! Other tips would be welcome; please tweet them at me or leave them on Hacker News.)