Chris Robshaw's team swept all before them in the Pool stages - the only club to make it six from six, scoring 28 tries in the process - but now it is sudden death time.
"This is our Champions League," said Harlequins Director of Rugby Conor O'Shea. "We are in Europe's top eight at the moment and we want to be in the top four come Monday morning.
"Home advantage is huge and we have to make the most of it, but Munster have a lot of experience and they will bring plenty of support.
"It is going to be a fabulous occasion at the Stoop. Munster will play with passion and we'll have to meet fire with fire. But we need to play our own game and our own brand of rugby.
"These are the games all the players want to be involved in and there are only 23 players lucky enough to be in the squad.
"You suddenly see a very clean bill of health from all the players when these games come around."