  Challenging environments comprise a range of scenarios, which share the fact
that it is extremely difficult to establish a communication link using
conventional technology due to many impairments typically associated with the
propagation medium and increased signal scattering. Specifically, underwater
and underground media are known to absorb electromagnetic radiation, which
heavily affects the overall path loss. Industrial and disaster environments can
be viewed as rich scattering environments with corresponding substantial
multipath propagation leading to intersymbol interference and deterioration of
signal quality. Although the challenges for the design of communication
networks, and specifically the Internet of Things (IoT), in such environments
are known, there is no common enabler or solution for all these applications.
Reconfigurable intelligent surfaces (RISs) have been introduced to improve the
signal propagation characteristics by focusing the signal power in the
preferred direction, thus making the communication environment 'smart'. While
the usual application of RIS is related to blockage avoidance, the very same
technique can be used to reduce the effect of multipath and even partially
compensate the signal absorption via passive beamforming. Due to the beneficial
properties of RIS, its use in challenging environments can become the
aforementioned enabler and a game changing technology. In this paper, we
discuss potential use cases, deployment strategies and design aspects for RIS
devices in underwater IoT, underground IoT as well as Industry 4.0 and
emergency networks. Furthermore, we provide a potential hardware architecture
and derive the expected signal quality. The numerical results reveal
substantial performance gains of up to 20 dB per decade. In addition, novel
research challenges to be addressed in this context are described.
