Best known for huge movie hits in the late 90s and early 00s, Hartnett is back on television screens for the first time in 15 years in the new gothic series.The programme is set in London in 1891, but it was filmed in Dublin.Hartnett told This Morning's Phillip and Holly: "I have compared (Dublin) to Vegas."It's one of those places that you want to go for a few days and then get out of there while your liver is still intact."We were working, so we didn't go out quite as often as I think a lot of people do when they are there."I am 35 now..." he joked.In Penny Dreadful, Hartnett stars alongside Bond actress Eva Green and former Dr Who star Billie Piper.Describing its premise, he said: "It involves a lot of characters from classic horror literature, (such as) Dorian Gray, Frankenstein, and Dracula."I play Ethan Chandler, the only American in the piece and you don't really know why he is there at the beginning, he is full of mystery.""What's really nice about this character is you don't really know much about him until further into the series."At the beginning of his career, Hartnett was known to millions as the Hollywood heartthrob who played action heroes in huge blockbusters, including Black Hawk Down and Pearl Harbour.But after numerous box office hits, the sheen of tinsletown wore thin for the actor and he withdrew from the limelight.Now back in the more mainstream world of TV and film, Hartnett said he was more comfortable within himself as an actor."I don't look back with regret as far as my career goes at all, and even my life," he said."Now at 35 I'm a lot less insecure about what people think of me, I'm more secure in who I am, so I'm able to play those bigger characters without fear of them representing me entirely."