The "Local Hot Bubble" (LHB) is an irregularly shaped low-density
 cavity in the ISM surrounding the sun. It is filled with a million
 degree hot plasma emitting soft X-rays.
 We have discovered a neutral dense filament located in the Local Hot
 Bubble. It has low kinetic temperatures, high space densities and is
 seen to cast a deep shadow in the ROSAT C-Band soft X-ray observations.
 The existence of neutral dense matter in the LHB is surprising in the
 first place. Either the filament formed recently in the LHB, or it did
 survive for a very long time; both explanations are a challenge to our
 understanding of the ISM.
 The filament must be cooled effectively to explain the observed low
 temperatures. We want to observe the most important cooling line, the
 CII(158um) 3P3/2 -> 3P1/2 transition of singly ionized carbon,
 and the OI(63um) 3P1 -> 3P2 transition of neutral oxygen. The
 combination of the parameters of both lines enable us to calculate
 the net cooling rate and to derive space densities and temperatures.
 We further want to study the radial variation of these parameters
 to analyse the physical properties of the interface of the cloud to
 the LHB and to look for possible confinement mechanisms.