Intramurous is great to explore. You can walk up the old fort ruins and at night look at the lit up makati skyline.
I had a great spa experience - Wensha Spa - located a small walk away from Sofitel Plaza. It's open 24x7 and for a about 1000 pesos, spend 6 hours in there, with body scrub, hot pools, steam, sauna, massage and free food thrown in. Awesome stuff.