where is the 'heart of stone'?

[thejames42]

in wintersun and i've read all the stones I can find. They reference the 'heart of stone' for a reward, but i have no clear where or what that is. i found the stone tree with the crazy elf, but nothing calls this the heart of stone, and I didn't find anything around it except a ring of protection +3. is it in wintersun, or another zone entirely like ivory tower? is it another zone I haven't discovered?

[Conquista]

its next to the spiked soldiers

[thejames42]

thanks!

for clarification, it's in the upper right quadrant of the map in the area with the impaled soldiers. there's a pile of stones just south of the waterfall which you can activate.