American traveling to Ireland, what are some must see areas, and what should I know before visiting your country?

Just to add I am a seasoned traveler through mostly SEA, parts of Africa and parts of Europe so I have no issues with traveling but I am curious if there are any must sees in Ireland and if there are certain customs that may be different than the US or other areas I have traveled?

My job forces me to travel a lot but this will be strictly a personal endeavor so I want to make the best of it.