consider this:
in 3, hosting the undernet servers underneath a hot spring was a 300 IQ play

the big servers need a huge amount of water for cooling and it's just right above, water can be dumped steaming hot into the bath continuously and no one bats an eye, the inn itself is also always filled with tourists and is public so anyone can come and go freely without suspicion so then the inns existence is purely as part of a cover for the servers (the servers built first, then the inn to help cover them up)

its advertised as a natural hot spring but you do get proof its faked talking to the prog in the lion comp when you catch him adding in oils and stuff

...now how does Mamoru get his wheelchair across the slippery hot spring floor to the hidden elevator without accidentally falling in and drowning? some questions are better left unanswered