"Eldorado Finale" is a song by Electric Light Orchestra

Electric Light Orchestra

Electric Light Orchestra were a British rock group from Birmingham who released eleven studio albums between 1971 and 1986 and another album in 2001. ELO were formed to accommodate Roy Wood and Jeff Lynne's desire to create modern rock and pop songs with classical overtones...

. The song appears as the finale to the Eldorado concept which includes a heavy orchestra

Orchestra

An orchestra is a sizable instrumental ensemble that contains sections of string, brass, woodwind, and percussion instruments. The term orchestra derives from the Greek ορχήστρα, the name for the area in front of an ancient Greek stage reserved for the Greek chorus...

 and a strong choir

Choir

A choir, chorale or chorus is a musical ensemble of singers. Choral music, in turn, is the music written specifically for such an ensemble to perform.A body of singers who perform together as a group is called a choir or chorus...

. The song did appear on the boxset, Flashback.

"I like the heavy chords and the slightly daft ending, where you hear the double bass players packing up their basses, because they wouldn't play another millisecond past the allotted moment."
Jeff Lynne (2000 - Flashback)

"This is a bit like Eldorado Overture

Eldorado Overture

"Eldorado Overture" is the opening track on Electric Light Orchestra's 1974 concept album Eldorado.It was a new experience for Jeff Lynne to use a full orchestra and choir for the band's songs. The opening starts with haunting sounds provided by Richard Tandy on the synthesizer...

but goes to many more places."
Jeff Lynne (2001 - Eldorado Remaster)