Welsh team officials have championed Saturday's RaboDirect PRO12 double-header at the Millennium Stadium, Cardiff.
Newport Gwent Dragons and the Scarlets will launch Saturday's action before Cardiff Blues take on the Ospreys - and 30,000 tickets have already been sold to what is being billed as 'Judgment Day.'
"This is a big occasion, one that we are looking forward to," Blues rugby director Phil Davies said.
"We will be playing at an iconic venue and trying to keep the feelgood factor of Welsh rugby going."
Dragons boss Darren Edwards added: "I think it is a fantastic concept. I was fortunate enough to play for London Irish in the first London double-header, and every year it has grown.
"Coming to the Millennium Stadium, with the roof closed and lots of spectators, it should be a great occasion we can all embrace and enjoy."
Welsh rugby is currently riding the wave after Rob Howley's national side snatched the RBS Six Nations title from England's grasp in the same stadium earlier in the month.