Drithelm was just your average Northumbrian guy, until he died and came back to life. Thereafter, he split his earthly goods into three lots, one for his family, one for his children, and one for the poor, and became a monk. He shared his vision of the afterlife –its rewards and its punishments– only to those he thought would heed its message.
He spent most of his time in prayer and mortification, often combining the two by praying in the frozen river nearby. To quote the Venerable Bede:
And as that place lay on the bank of the river, he was wont often to go into the same to do penance in his body, and many times to dip quite under the water, and to continue saying psalms or prayers in the same as long as he could endure it, standing still sometimes up to the middle… And when in the winter the half-broken pieces of ice were swimming about him, which he had himself broken, to make room to stand or dip himself in the river, those who beheld it would say, “It is wonderful, brother Drithelm, (for so he was called,) that you are able to endure such violent cold;” he simply answered, for he was a man of much simplicity and indifferent wit, “I have seen greater cold.” And when they said, “It is strange that you will endure such austerity;” he replied, “I have seen more austerity.”