The first portal made for the purpose of transferring the wyrms to the Otherworld was at the Côr y Cewri, now known as Stonehenge.
The Portal of Stonehenge connects Britain to present day Darklands.
The enchanting sounds of the giant stones (now known as Mystical Acoustics) were used to open the portal which was previously used by the elves.
The Stonehenge turned out to be a one-way portal. That is, once the creatures were transported to the islands, there was no way back.