This treasure chamber makes a would-be thief work much harder for that haul.
Wondrous Item 25,000 gp
You can spend 24 hours attuning the vault to yourself. Any item left in the vault for at least 24 hours weighs five times normal for creatures not attuned to the vault until it has been outside the vault for 24 hours. In addition, unattuned creatures cannot fly within the vault.
Published in Dragon Magazine 383, page(s) 46.