“The Castle In The Air” stands out from its first few seconds with Leah Senior narrating from the perspective of a traveler to Polygondwanaland, making it the only song on the album to feature her. From there, the complexity builds with twisting acoustic guitar lines and gravelly vocal harmonies. “The Castle In The Air” is the second song in a three track suite of “Polygondwanaland” > “The Castle In The Air” > “Deserted Dunes Welcome Weary Feet.”
On April 3rd, 2017, a Facebook user named “Blinky Bill” posted a link in a King Gizzard fan group to a playlist of demos on Soundcloud called “Polygondwanaland”, the first indication of the existence of the project. Included in the demos was “Polygondwanaland I+II+III” with a runtime of nine minutes and ten seconds. While the track was named “Polygondwanaland,” it contained the entire run of songs including “The Castle in the Air” which appears close to the album version, just without lyrics and synthesizers. The studio version of the track was recorded by Casey Hartnett at Flightless HQ and released on November 17th, 2017 as part of Polygondwanaland. The opening narration from Leah Senior would be referenced on the album’s cover. In 2021 “The Castle in the Air” would be name dropped in the song “Dreams” while a depiction of said castle made it into the video for “Ya Love.”
The earliest recorded performance was on 2018-5-24 at the Theatre Royal in Castlemaine, Victoria (without acoustic guitar) alongside “Deserted Dunes Welcome Weary Feet,” though their placements were reversed compared to the album. This would create a medley of material from the end of 2017: “Crumbling Castle” > “The Fourth Colour” > “Deserted Dunes Welcome Weary Feet” > “The Castle In The Air” > “Muddy Water.” On stage “The Castle In The Air” would be shortened to only a bit over a minute to make a quick change into “Muddy Water.” Since its debut it has served its role within sets but has not been played since 2019-11-21 at the Modern Sky Lab in Shanghai.