This unique distinction goes to about 40 metres wide small volcanic island called -
Vulcan Point Island
located in - Crater Lake (about 1.9 km across)
located in - Volcano Island (aka Taal Valcano) (about 5-6 km wide)
located in - Taal Lake (about 16 km across)
located in - Taal Caldera on Luzon Island, Philippines.
Following image explains this complex location;
A panoramic view of same;
More info at Philippine Institute of Volcanology and Seismology Taal Volcano Web page and Wikipedia
View location in Google Earth Google Maps. (It is the small white blob in black lake).
Credits: Redeemed (GEC Link)