More details about the Istana Open House on the NParks website and the Istana website.
Time: 10am to 4pm every hour.
Costs:
$2 for each child aged 3 years & above.
$4 for Singaporeans / PRs aged 13 and above.
$10 for foreigners (aged 13 and above).
Family package, $12 for Singaporeans / PRs (family of 4) and $30 for foreigners (family of 4).
Please make the payment on the spot on the event date itself.
Each guided walk group can take up to 12 people
Website: http://www.nparks.gov.sg/