We’ve all seen them, now it’s your time to make them. Forced perspective is playing with object in the foreground and background of each other. By placing objects at different distanced from your camera you can play with how large they looks. Have fun make something look huge, or tiny.
Forced perspective is used all the time in less touristy way. It was used in the Lord of The Rings trilogy to make small characters seem short next to equal size actors. The trick here is eye lines. If you're using a model it may be a good idea to have them look where this oddly sized object is pretending to be.
Here's a cool video showing how they did it in the Lord of The Rings trilogy.