Here are the relevant quotes:
I
“The truth is that most of what we know of hell and its eternity comes from the lips of our Lord and Savior, Jesus Christ. And he uses terms that are unequivocal. Pope St. John Paul II, in his book Crossing the Threshold of Hope, says it succinctly:
“The words of Christ are unequivocal. In Matthew’s Gospel [Christ] speaks clearly of those who will go to eternal punishment (cf. Matt. 25:46).
…
“The teaching of the Church affirms the existence of hell and its eternity (Catechism, Par. 1035).”
II
"Hell is primarily a state of being, but inasmuch as the souls there will have bodies after the resurrection of the dead, they will have location as well. So, in that sense, we can say hell is a ‘place’. In fact, we could say the same of heaven. But both heaven and hell are not ‘places’ in the sense that the people there could ‘leave’ and ‘return’. Inasmuch as these are states of being, ‘heaven’ and ‘hell’ are present wherever the saints and damned are.”
The rest of the article is full of references to Scripture and the Catechism.