Six sense bases
The drawing of a house with six openings represents the sixfold sense base. These are the gateways through which the mind makes contact with objects. These are the senses of sight, hearing, taste, smell, touch and the mind sense. Each sense has its physical base and each its particular object.
It is significant that Buddhist philosophy always lists six senses; the mind-sense taking ideas as its object. This makes an interesting contemplation; to think of ideas as something we sense rather than something we do.
It should also be noted that the house is empty.