The new Cryogenic Underground (C2U) facility: an overview The low radioactivity cryostat of CROSS (Cryoconcept) is equipped with a Cryomech PT415 pulse-tube. A special technology (Ultra Quiet Technology) is employed to mitigate the pulse tube vibrations. The cooling process take place in two phases: - precooling: from 300 K to 4 K obtained by circulating a 3He/4He mixture at high flow rate (17 mmol/s) - standard cooling: from 4 K to 10 mK, by using a dilution unit closed-cycle (condensation at 2 mmol/s). The dilution unit has a cooling power of about 6 uW at 20 mK and 340 uW at 100 mK, and can reach temperatures below 10 mK over an experimental volume of 600 cm length and 30 cm diameter. The cryostat cools down to 4 K without any exchange gas: 120 kg of internal lead-copper shielding plus few tens of kg of low temperatures detectors/holders are ready in 55 hours to be further cooled down 10 mK. In few hours the detectors reach the 20 mK temperature region and are ready to study. The Mixing Chamber temperature is stabilized around 12 mK with temperature fluctuation within 10 uK. The best detector working point is searched and noise optimization studies begin... We performed a campaign of "seismic" measurement at the installation site to built the best strategy to place the cryostat and decouple from environmental vibrations. Since the ground floor at LSC is an extremely calm reference frame (except human activity), the cryostat is referenced to the floor. With high sensitivity accelerometers we further characterized the vibration profile of the 10 mK replica plate, where detectors are installed, with pulse tube ON/OFF. Along the radial direction r, the pulse tube high order harmonics are not totally cancelled, despite the UQT system. These residual components are mainly due to the positioning/fixation of the rotary valve. An upgrade of the system is under study. The Mixing Chamber is regulated via a PID system, which typically delivers a power of about 200 nW (5.5 uW) to stay at 10 mK (20 mK). Temperature/noise stabilities are key parameters to perform high quality, long-living bolometric searches. The cryostat is equipped with shielded, twisted pair manganin wires. The wiring goes (without any interruption) from 300 K down to 10 mK: here the conductors are thermalized via Kapton pads thermally anchored to the cold stage. The cables are thermalized at every cryostat cold stages by mechanical clamping of the shielding. Experimental Space Tripode (to hold the pulse-tube head) External 25 cm thick lead shielding Rotary Valve New low noise electronics Hydroformed bellow Pulse Tube head 300 K flange The pulse tube head is coupled to the cryostat via a supple hydro-formed bellow and is firmly kept by a tripode rigid frame. The pulse tube cold stages are thermally linked to the cryostat cold stages by gas loaded exchangers which prevent any mechanical contacts. The cryostat is mechanically referenced to the floor: it is tighten to a 10 ton lead-brick loaded platform. Bricks constitute the low radioactivity external lead-shielding (25 cm thick) which protects the internal experimental volume from the external radioactivity. An internal lead socket (120 kg weight), cooled down to temperatures as low as 800 mK, shields the experimental volume from the dilution unit and cryostat upper parts (no low radioactivity materials). From below, the experimental volume is protected by a 25 cm thick lead socket. Lead socket Front-end: 6 detectors per card, directly plugged to the cryostat connector box Detectors are equipped with high resistivity sensors (Ge-NTD, 1-10 Mohm resistance). The sensor signals are read by low-noise, room-temperature amplifiers. The sensor bias current circuitries (typ: 10 pA-30 nA range) is also embedded in the amplifier modules. The signals are afterwards shaped with a programmable Bessel filter and digitized with 24 bit precision ADC (+- 10.25 V dynamic range, 5kHz sampling frequency). New electronic intrinsic noise 10