This is an incredibly old site. We were impressed.
On a wet and miserable day there was no problem with getting a ticket. Believe me you need warm clothes and raincoats as most of the tour is outdoors.
When you do go into the passage of the tomb/temple it is very tight - not for claustrophobes!
The guide was informative although a little difficult to hear over the noise of the rain on umbrellas and the wind!
We visited in Sept and (surprise) it was wet in Ireland. It is a fair walk from the car park to the visitor centre and then you have to ride one of their busses to the site itself.
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