UK clubbers have returned to the dance floor for the first time since the pandemic began, as part of trials to see how venues can reopen.
Some 6,000 partygoers are expected at a warehouse in Liverpool across a two-day event that started on Friday.
Ticket-holders don't need to socially distance or wear face coverings, but they'll need a negative Covid test result before being allowed in.
Liverpool is also set to host the UK's first restriction-free gig since Covid.
Circus's The First Dance club nights, which are part of a series of government trials on crowd safety during Covid, are at the Bramley-Moore Dock warehouse.
Sven Väth, the Blessed Madonna and Jayda G are all performing on Friday night. Fatboy Slim is headlining on Saturday.
Coronavirus has crippled the nightclub industry, with a recent report finding UK clubs have been forced to make 51% of their staff redundant since last year. In comparison, bars and pubs have axed 32% and 25% of their workers respectively.
Clubs will have been closed for 15 months by June, when it is hoped all legal restrictions on social contact will be lifted in England.
Scientists are using this weekend's event to look at whether crowds mixing and dancing indoors increases transmission of the virus.
Public health expert Prof Iain Buchan, who is leading the research, tells Newsbeat his team will use carbon dioxide monitors to detect "pockets of stale air" in the venue.
There will be also be small cameras for the scientists to monitor people's movements.
Prof Buchan says a key question the trial event needs to answer is: "With all of those measures in place, do people still enjoy themselves?"
"That's a really important part of making these events sustainable," he says.
Those attending the club nights must have a negative Covid test result from a lateral flow test within 24 hours of the start of the event.
The test cannot be done at home but instead must be carried out at a local testing centre. This is because the government wants to look at the role these centres could play as big events return.
Partygoers will also be encouraged to take a PCR test five days after their night out, to make sure any spread of the virus is properly monitored.
'One to remember'
Only those living in the Liverpool City Region and showing no sign of Covid symptoms were eligible to apply for tickets.
Jade Edwards is one of those with a ticket. The 28-year-old barista from Liverpool tells Newsbeat she feels "emotional" that her hometown has been given the opportunity to host a trial event.
Jade says it's been two years since she properly went clubbing.
"I'm excited to see Yousef... it's going to be one to remember," she adds.
Sport has already been trialling the return of crowds, with events including the World Snooker Championship and the FA Cup.
Liverpool has been at the forefront of the government's trials on crowd safety - on Sunday, Blossoms will be among the bands to perform to a crowd of 5,000 fans at an outdoor gig at Sefton Park.
The site can usually host 7,500 people.
As with the club nights, lateral flow tests will be required beforehand but social distancing and face coverings won't be needed once people arrive.
The gig is being hosted by Festival Republic, which is also behind Reading and Leeds Festival.
Melvin Benn, Festival Republic's managing director, doesn't believe the event carries a public health risk.
"If there had been concern the event would produce a spike, the public health director in Liverpool would have suggested to us that it wasn't a good idea to go ahead," he says.