Undersafe is a system which will provide constant, round-the-clock monitoring of environmental and other conditions in underground sites open for recreational and tourist purposes. The UnderSafe system will be based on wireless technologies. The objective is to develop a safety system which will detect and provide early warning about a number of conditions that can pose a danger to those underground. It will be based on low cost and low consumption communication technology, which offers robust conditions in front of electromagnetic disturbances. The basic system will include a number of nodes along the underground space, located in the upper limits of the walls (Static Nodes). The different nodes have to be situated sight-to-sight with at least 2 nodes, accomplishing the communication channel. Visitors will wear specifically designed nodes (mobile nodes), which will communicate with static nodes. The system will include the following characteristics and capabilities: i) Only power wire is needed, in order to power supply to wall routers; ii) Low maintenance cost; iii) Low cost; iv) Robustness: IP compliant for hazardous ambient; v) Static node sensing of temperature, humidity, light, pressure, sound and gas (O, CO, CO2) sensing capabilities; vi) specialized static nodes for vibration sensing and landslide detection vii) mobile nodes.