Some illusions are created naturally or unintentionally. Other illusions are created deliberately.

Illusion - levitating boat Illusion - levitating boats

Flying boats

Illusion - cat bag
Illusion - by Aakash Nihalani

The TARDIS illusion by Richard Gentle

Originally built inside a single garage with a side door from a small yard. Opening the TARDIS doors (left side) led into a larger room...

Illusion - TARDIS

The facing view is part illusion, where the panel is reflected in a mirror to the right, placed at a right angle to the panel.

Illusion - campervan car

...a workshop:

After moving house, the TARDIS was re-built in the living room (below). Since there were only ever 2 panels, a large front and a half-width side, the TARDIS turned into a cupboard:

Illusion - TARDIS Illusion - TARDIS

The illusion is designed to work from one specific angle, controlled by the approach to the room. The illusion in the living room (above) works particularly well, since the approach is along a narrow corridor. Furthermore, the furniture in the room is not reflected in the mirror. However, viewed from the side, you can see that this TARDIS is actually bigger on the outside than it is in the inside!
Illusion - book drawing Illusion - arch
Illusion - reality

Illusion - tree trunk

Illusion - head
Illusion - street twist

Illusion - reflection

Illusion - reflection