You are in a room by yourself and someone walks into the room, asks you to find the temperature, and leaves. How would you find the temperature in the room without leaving the room?

Cut a 5cm*5cm*5cm ice cube from the refrigerator, and test how long it take for it to melt completely.

Find two equal size ice cubes, for the first one, wait till it melts completely(0 ℃) , heat it till it boils, record the time t1. For the second one, wait long enough till the water has the same temperature with the room, than heat it till it boils, record the time t2. The room temperature is 100*t2/t1.