The problem with many pizza places is that they only sell whole pies. Many hotels now have mini fridges in the rooms, so storing leftovers isn't bad. But, how do you reheat a slice of pizza in a hotel room? Ideas?

Many hotels have microwaves in the breakfast room or front desk; not optimal, but works in a pinch.

Just eat it cold? I love cold pizza but YMMV

Hairdryer does sound the obvious solution.

Use the iron - hold upside down, place foil on iron, pizza on foil.

Although I loathe the results, a good percentage of hotels which have a mini fridge also have a microwave.

I have actually seen this happen with scotch pancakes!

This. I've done this before. Actually works great.

I will have to try that. It is kinds pizza shaped, isn't it.

Use the microwave if there is one in the room. Some hotels have microwaves in common areas, for example near a market/pantry outlet that sells snacks. Policy differs whether hotel guests can use these microwaves for food not purchased there, so be sure to ask first and don't make a mess or consume the pizza in a common area.

Campus legend says that irons can be used to cook food. I know they work for things that otherwise would be fried without fat or grilled, such as steak, but it can make a mess of the iron.

Hairdryers are good for drying clothes in a pinch, but I don't think most of them are hot enough to make the food hot rather than vaguely lukewarm.

If the hotel water is really hot, you could experiment with putting the pizza in something waterproof, such as a 3-1-1 storage baggie, and immersing in very hot water. You could even try the same if the hotel room is equipped with a kettle or even a coffee maker that can be used to heat water for tea, and similarly if you travel with an immersion water heating coil.

Sous vide pizza....

Interesting thought....

If you have a rental car, you can also reheat it on the warm engine--like using the iron, but with more surface area. (Definitely use the foil.)

There was a Mythbusters episode you can use for reference, and cooking/reheating with a car engine has also come up on Car Talk.

(OK, admittedly this is outside your hotel room, but so is the lobby microwave. )

If your bathroom has a heat lamp, use the heat lamp and hold the pizza right by it, but not touching. Yes, it works. In some hotels, you can balance the pizza box on the door and shower curtain rod (I've done this).

cold pizza is perfectly fine given all this effort you are talking about

The easiest thing to do us just go to Papa Johns and give them $5 for a fresh Hot-n-Ready pizza.

^ I rarely bother to reheat pizza even if I'm at home!