If you're thinking of a lair as a hidden or secret place:
* Haven: A safe and peaceful place.
* Sanctuary: A place of refuge or safety.
* Refuge: A place of shelter or protection.
* Home: A comfortable and familiar place.
If you're thinking of a lair as a dwelling place associated with evil or danger:
* Paradise: A place of perfect happiness and peace.
* Utopia: An ideal society.
* Elysium: A place of perfect happiness in the afterlife.
If you're thinking of a lair as a place of secrecy and deception:
* Transparency: Openness and honesty.
* Honesty: Truthfulness and sincerity.
* Integrity: Moral soundness and uprightness.
The best opposite word for "lair" will depend on the specific context in which you are using it.