The demand for intelligent networks and diversified computing applications is driving the need for 6G communication networks. Additionally, the innovative 6G applications will impose stringent requirements that will be difficult to satisfy with fixed, pre-deployed infrastructures. The characteristics of unmanned aerial vehicles (UAVs) make them an essential component of the outdoor and indoor 6G infrastructures. UAVs can form indoor-flying networks (IFNs) to support the indoor 6G infrastructure. This article introduces the concept of IFNs, covers the application scenarios of IFNs, discusses the enabling technologies to effectively deploy IFNs, highlights technical challenges, and presents potential research opportunities. Additionally, this article presents a use case scenario that employs machine learning techniques to enable more efficient modulation and coding to enable IFNs in the manufacturing industry.