Hal's secret high: the hilltop tunnelled by design
The Academy's tennis courts' Lung's Pump Room is underground and accessible only by tunnel. E.T.A. is abundantly, embranchingly tunnelled. This is by design.
Context
E.T.A.'s campus is a purpose-built body-machine with its own circulatory plumbing: "abundantly, embranchingly tunnelled," and pointedly "by design." The infrastructure that serves the tennis plant — Lung, Pump Room, laundry, weight room, all threaded underground — is the physical form of an institution organized entirely around producing and servicing athletic bodies, right down to a subterranean nervous system only the smallest kids' Tunnel Club fully knows.