This chapter provides an overview of unusual multifunctional, specialty single-mode fibers-macrohole fibers, multicore fibers, fibers with internal electrodes, and fibers for high-temperature resistant fiber Bragg gratings. Macrohole fibers belong to the group of microstructured fibers, which encompass a wide variety of fibers with air holes or other structures extending in the axial direction. Functions performed using macrostructured fibers include supercontinuum generation in tapered hole fibers, dispersion management, fibers with decreased bend loss for compact optical fiber wiring, and fibers for polarimetric sensing, and lasers. The introduction of materials in the holes adds the possibility of manipulating the guiding properties of the fiber. This can be achieved by interaction of the guided mode with actively controllable materials in the holes or by using the inserted materials for other active functions, such as a metal electrode to implement electro-optic control of the fiber. The proposed applications for multicore fibers span over lasers and amplifiers, transport fibers for broadband communications, passive, and active fiber optic components such as filters, multiplexers, and various kinds of sensors. The ultimate multicore fiber is the image fiber used in endoscopes and other such devices.