Located at Ilije Sarake 4. It is very easy to find, just behind Dubrovnik cathedral.
When you are on Pile station, just in front of Old Town, head northeast on Ul. Vrata od Pila.
https://maps.google.ca/maps?saddr=p%C3%ADle+near+Dubrovnik,+Croatia&daddr=Sponza+Palace,+Dubrovnik,+Croatia+to:Ulica+Ilije+Sarake+4,+Op%C4%87ina+Dubrovnik,+Croatia&hl=en&ie=UTF8&ll=42.640462,18.108891&spn=0.005272,0.010332&sll=42.640459,18.108739&sspn=0.005272,0.010332&geocode=FWKpigIdoEoUASHEQofApoQixCkL5MtkLQtMEzHEQofApoQixA%3BFUemigIdolgUASGoa6bYH839_CmRbmABMwtMEzGoa6bYH839_A%3BFfGfigId41cUASnfS4vKMwtMEzHUnSef72WVqQ&oq=Ilije+Sarake+4&dirflg=w&mra=ls&t=m&z=17