Evelyn Underhill was an English Anglo-Catholic writer and pacifist known for her numerous works on religion and spiritual practice, in particular Christian mysticism.
In the English-speaking world, she was one of the most widely read writers on such matters in the first half of the twentieth century. No other book of its type—until the appearance in 1946 of Aldous Huxley's The Perennial Philosophy—met with success to match that of her best-known work, Mysticism, published in 1911.
Concerning the Inner Life was very good read. She provides many helpful reasons and reminders for why we need to keep a good prayer life.
The House of the Soul was also enjoyable, but as an Evangelical Christian I found some of her Catholic mysticism to be a impeding on the general message of the book. I think some of her metaphors were very helpful, but some of them felt almost neoplatonic, and others felt entrenched in a problematic pelagian Catholic theology.