Sycrus Key FFIII Art
The key that opens the way to the Crystal Tower.

The Sycrus Key (シルクスの鍵, Shirukusu no Kagi?, lit. Sylks Key), also known as SylxKey, is a key item in Final Fantasy III, which is required to open the way to Crystal Tower. It can be obtained by defeating Doga and Unei at Doga's Grotto.