We got to the rental car agency, where we were promptly stuck with fees and insurance of $320. There was no getting out of it, even on a car that was "included" in our travel package. In retrospect, I DID feel good (for the first time in my life) about having full, zero deductible coverage on a rental car, even though (spoiler alert) I didn't end up needing it.
I figured we would basically get a clown car, and I was right. Somehow we made it work.
For the record, I did NOT put that ding in the car. Not only was the car tiny, but it was...well-worn.
After taking the pictures for posterity (and, frankly, to cover my ass), we got in the car. Not only are you driving on the opposite side of the road--you're SITTING on the opposite side of the car. This is where I became incredibly glad we upgraded our car to an automatic. I can't imagine trying to pick up driving on the wrong side and remembering how to drive a stick...with the wrong hand.
The first trip was nerve-racking. I had been up all night, so I wasn't very focused to begin with. The roads are actually marked well, but differently--everything is painted white, so the direction of travel is even more confusing, especially when there are an odd number of lanes on the road (which happened a LOT).
Then, we got to the first roundabout. Holy crap. Transposing everything in my head, looking at the hundreds of cars bearing down, flashes of European Vacation going through my brain...wait, where is Swords Road? Google Maps says take Swords Road; there is no Swords Road! Gah! Turns out, all the roads on the highway system have been assigned numbers, and the numbers appear on the signs now. We figured it out and finally made it to the hotel that we couldn't check into for 6 more hours. We parked the car for the day, because we were told in no uncertain terms not to drive in Dublin.
We also obtained a GPS for the trip, but the device had two substantial glitches. First, the software was out of date, so any roads constructed in the last few years did not appear on its maps. Turns out they have built a bunch of roads recently. We were frequently depicted as driving through some sort of sheep field, no road in sight. Second, the GPS didn't seem to have data on road width, so on at least a half-dozen occasions it tried to send us down a road that was more narrow than my driveway. Nevertheless, we were glad to have it, even when Emily the Brit's condescending voice told us she was "reCALCulating".
Anyway, after the first day, things got better. I figured out roundabouts, city driving, and the fact that a 100 km/h (60 mph) speed limit does not mean you will physically be able to go that fast. Unlike here in the states, you will not see signs telling you how far you must slow down to take that curve ahead. Occasionally a construction truck will barrel around the corner at you, and you better be ready. It was definitely not the least-stressful way to see the country, as there were very few moments of relaxation behind the wheel.
But I wouldn't change a thing. In the end, I drove 726 miles overall (my fiancee was quite alright with not driving, thank you very much), and we saw--on our own time--all of the stuff below. Those poor suckers on the tour buses missed it all...and this is just the proverbial tip of the iceberg.