From Destinypedia, the Destiny wiki
Apothecary is a location within the Court of Savathûn. It is located deep within Savathûn's fortress and serves as a testing ground for the Lucent Brood's most wretched experiments involving the Light. It is mainly reached by going through the Alluring Curtain, but a portal hidden inside leads to the Temple of the Wrathful. A portal on the top floor leads to the Court of Thorns, though the floor itself cannot be reached by ascending the building in Patrol.
The Guardian stormed the Apothecary during the final hours of their investigation of the Throne World. They clashed with the many forces of the Lucent Brood lurking within, including Savathûn's Right Hand, and emerged victorious, claiming a shard of the crystal that encased the Witch Queen during her time in the custody of the Awoken. They would later return to the wing in their quest to provide a host to Savathûn's Worm, stealing the captured Light from inside of it.