Fairy Gnoc

Apparently a sidhe (shee) is the portal to the Otherworld.

Gnoc is the word for "a hill" and can be a sidhe hill or a regular dirt hill.

If you would like to know more about Gnocs and the Sidhe take a look at these sites:

http://celticsociety.freeservers.com/sidhe.html

http://www.csun.edu/~hceng029/yeats/funaro.html

http://celticanamcara.blogspot.com/2010/03/aos-si-kings-and-queens-of-fairies.html

http://www.sacred-texts.com/neu/celt/ali/ali222.htm

https://en.wikipedia.org/wiki/Aos_S%C3%AD