Absolutely delightful place, even better than the pictures suggest. Great view over the castle (with sunrise view as an added bonus), comfortable and tastefully decorated space. The kitchen had everything you need (including French and Italian coffee makers, toaster, water cooker). Wonderful bed!
Two metro lines (blue and green) are 1 and 5 minutes walk away, and within 15 minutes walk you're in Alfama, Barrio Alto or on the seaside (but, of course, this being Lisbon there's quite a height difference to be covered:-). And actually all the main sights except Belem are walkable. And despite being in the center the apartment is quiet, with only the occasional ambulance to the hospital next door being noisy.
There's a pretty decent supermarket down at Praça Martim Moniz. Local restaurants seem to be all asian, but as said you can get to any downtown restaurant easily.