On 9 July 1937 a terrible explosion occurred here on Vallisaari, in a sheltered area that later became known as The Valley of Death. Tonnes of ammunition exploded, and fragments were flung as far as the neighbouring island of Suomenlinna. Everyone on the island fled for their lives, but eight people were killed instantly, and four more died later of their injuries in hospital. The head of the Defence Ministry’s armaments department Engineer Colonel Aleksanteri Huuri suffered from such traumatic shock that he too died a week later.
The cause of the explosion still remains unknown, but it may have been due to the careless handling of explosives, and sabotage is not out of the question. Some explosives still remain here in the Valley of Death to this day, but visitors observing safety warnings have no reason to fear.