I dont know anywhere that you could just unload horses and go riding, sorry... I resort to just hacking my horse around on the roads.
Generally you could find places in Galway and Wicklow that do trekking. You would get a very different environment as in Wicklow you would be (mostly) in the mountains, and in Galway you'd be (mostly) on the beach. There is a place in Laois that offers western riding, which offer overnights and packages - havent used any of them myself but know they are there. There is also a place in Waterford that offers beach trekking.
Generally all of these horses are buses and know the route inside and out so you would be perfectly fine. There is a trekking center not to far from me (Meath) but can't think of the name, or how much it costs. They also have a cross country course if you were up for that. Castle Leslie is meant to be fab, but pricey.
Hope this helps a bit :)
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