Please keep the door open.

To cause to remain in a specified state or condition.
Keep the room clean.
Keep your voice down.
Keep the change.
keep quiet
keep going
keep in touch
maintain
preserve
hold
The old castle has a well-protected keep.

A place where something is stored or maintained.
The keep held valuable supplies.
Guard the keep at all costs.
The keep was a safe refuge.
castle keep
fortress keep
protect the keep
citadel
fortification
stronghold