Nicodemus and the other rats built their home under the rosebush, how is it described in the novel, Mrs. Frisby and the Rats of Nimh?

Nicodemus and the other rats have constructed their own fantastical world beneath the rosebush on the Fitzgibbon farm. They have a fully organized headquarters in a cave, using electricity to power lights, an elevator, air ducts, and a radio. They also have a fully stocked library and meet in a large assembly hall to discuss the future of their civilization.