The Reds' win over Borussia Dortmund will live long in the memory.
Anfield well and truly reinforced its reputation as a fervent location on European nights as the Reds supporters welcomed the equally-passionate Dortmund fans to Merseyside for what was a special night - and it started even before kickoff.
"The atmosphere was like what I heard about. It was incredible before the game driving through the streets," Allen, a £15 million signing in 2012, told The Mail.
"Nobody told me that would happen. Some people have a whole career in football and not experience a game like this one."
Both sets belted out a heartwarming rendition of 'You'll Never Walk Alone' as a preamble, before the Bundesliga side - who drew 1-1 in the quarter-final first leg - moved into a shock 2-0 lead inside 10 minutes.
Jurgen Klopp's troops, trailing 3-1 on aggregate and needing at least three second-half goals, threw themselves a lifeline when Divock Origi pulled one back two minutes after the break, but a slick finish from Marco Reus shortly after restored the visitors' advantage.
Needing to score three times in the final half-an-hour, Philippe Coutinho drove home on 66 minutes, before Mamadou Sakho nodded home a third with 12 minutes to go to leave his side needing just one - and Dejan Lovren found it in stoppage time as Anfield erupted.
Klopp and co will meet Villarreal in the semi-final of the competition.