Having played on two Lions tours himself, in 1997 and 2005, Rowntree is well placed to talk about the fervour of local opposition on the big day. But he expects his pack to be able to handle all that is thrown at them.
"If I was one of the players in the Royal XV, I would be throwing myself into those early collisions and tackles. It is a massive game for them," said Rowntree.
"I expect an early onslaught from the Royal team. A lot of these guys won't get the chance to play against the Lions again and they have been given the first opportunity of this tour.
"They will fancy their chances as it's our first outing and we have not long been thrown together. They will be the underdogs and I'm sure they will want to prove a point or two to us."
Rowntree is looking to his forwards to set a platform for a good opening performance and he admits to being excited by some of the combinations.
"The front row excites me. I've been very impressed by the way the Welsh boys, Matthew Rees and Adam Jones, have turned up and gone about their work," said Rowntree.
"Adam has made giant strides physically in the last few years. I was surprised at how big and muscular he is.
"His game as come on as a scrummager, he is defensively very good and his involvement in the wider game has also developed well. You saw that from the way he delivered the scoring pass for a welsh try against England in the Six Nations. "Andrew Sheridan is also back playing very well. By his own admission he didn't have a good Autumn Series, but by the end of the Six Nations he was back to his best."
Another player who has impressed Rowntree has been England lock Simon Shaw, who was a team mate of his on the 1997 Lions tour to South Africa. He will pack down alongside tour skipper Paul O'Connell in the opening game.
"Can you believe that Simon was out here playing with the Lions 12 years ago? But he is still in very good nick and playing very well," said Rowntree.
"I'm delighted he is here with us because we are going to need the characteristics he brings to the game on this tour."