Festival goers attend day one of the Parklife Festival at Heaton Park on June 9, 2018 in Manchester, England. (Photo by Mercury Press)

Fireworks explode over a floating Christmas tree in Lagoa Lake in Rio de Janeiro. (Photo by Victor R. Caivano/Associated Press)

Fisherwomen laying barrels with salt in preparation for herring curing, 1937. (Photo by Topical Press Agency)

A white whale wears a wreath at the Hakkeijima Sea Paradise aquarium-amusement park complex in Yokohama, Japan, on October 3, 2012. (Photo by Associated Press)

Two stags fight in a wildlife park in Aurach near Kitzbuehel, in the Austrian province of Tyrol. (Photo by Kerstin Joensson/Associated Press)

Coffins are lined up near the wreckage of the bus, on July 29, 2013. (Photo by Salvatore Laporta/Associated Press)

Revellers enjoy during New Year celebrations in Manchester, England on January 1, 2019. (Photo by Mercury Press)

The Haʻikū Stairs, also known as the Stairway to Heaven or Haʻikū Ladder, is a steep hiking trail on the island of Oʻahu. The trail began as a wooden ladder spiked to the cliff on the south side of the Haʻikū Valley. It was installed in 1942 to enable antenna cables to be strung from one side of the cliffs above Haʻikū Valley to the other. A building to provide a continuous communication link between Wahiawā and Haʻikū Valley Naval Radio Station was constructed at the peak of Puʻukeahiakahoe, elevation about 2,800 feet (850 m). The antennae transmitted very low frequency radio signals from a 200,000-watt Alexanderson alternator in the center of Haʻikū valley. The signals could reach US Navy submarines as far away as Tokyo Bay while the submarines were submerged.