I am the ghost of Shadwell Stair.
Along the wharves by the water-house,
And through the cavernous slaughter-house,
I am the shadow that walks there.
Yet I have flesh both firm and cool,
And eyes tumultuous as the gems
Of moons and lamps in the full Thames
This could have several meanings. Owen is a compassionate man and therefore an anonymous but empathetic observer, a ‘shadow’ watching people living difficult, impoverished lives. But it could be his spiritual self seeking escape. 
 Given the time in which he lived, it could also be his guilty self, ashamed of his need for sexual comfort. It is notable that many young soldiers sought sexual experience when on leave, not wishing to die virgins.