The Obsidian Tower

It appeared in 1027 a few months after the 7 Heroes destroyed Torog. The Obsidian Tower rose from the ground shaking the land and pulsing with green and purple magical energy. Where did it come from? What powers had sent it? No one knew. Forces of Gaulthoth and the remaining four members of the 7 Heroes went to face whatever this new horror was. But nothing ever happened. No one was able to find a way in, and the magical energy stopped after some time. After a few years of watching, the country simply left it alone, and created a canal in order for ships to avoid it passing the river. People now wonder what lies dormmate inside and if there is any treasure.