When Nintendo first started development on the Legend of Zelda: Ocarina of Time, Shigeru Miyamoto and the development team behind the project envisioned a much different game than what we finally got in 1998.
Instead of an expansive overworld in which players could spend hours exploring, the original plan was for all the dungeons to be accessed through paintings hanging inside Ganon's Castle, just like Super Mario 64 in which players accessed each stage through paintings hanging in Peach's Castle.
Thankfully the development team realized how this plan would run counter to the theme of exploration, which has been a main staple of the series since the original installment on the NES and so they decided to bring back an expansive overworld. Thank heavens; I can't imagine Ocarina of Time without riding Epona through Hyrule Field!
A relic of the original plan remains in the boss fight at the end of the forest temple in which Pantom Ganon travels in between paintings. Also, three of the four poes you must defeat in that temple emerge from paintings.
Source: Hyrule Historia.