Pembroke Castle has reopened to the public 24 hours after 999 crews were called in amid safety concerns about a suspicious container.
Dyfed-Powys Police said an initial inspection by experts concluded the container did not contain dangerous liquid.
However, it has been taken away for further forensic examination.
Police thanked the public for their patience while the "time-consuming, but necessary work was carried out".
Specialist support was provided by the Mid and West Wales fire service and the Welsh Ambulance service's Hazardous Area Response Team.
Police were initially called to Castle Terrace at about 13:00 BST on Friday, leading to the closure of the castle.