Thanks for the tip about Route 9 versus Taconic Parkway. Depending on the time and what I stop at (Storm King looks intriguing) and what time the Kykuit tours are on I could drive a bit further, maybe to Beacon and come back from there.

I'm a bit iffy about renting in Manhattan. The traffic and having to get used to a left hand drive in a busy place worries me.

Look for a rental agency on Broadway in the Bronx. I believe that there is one near 238th St. which is two blocks from the Major Deegan Expressway.

Love love love Hyde Park and all the FDR/Eleanor sites. Wonderful. And we had 3 meals at the CIA and all were amazing.

I agree about Hyde Park, especially the Roosevelt museum. However, with Kykuit and Storm King on the one-day itinerary, I don't think the OP will have enough time to make the stop there worthwhile. If the OP decides to extend her Hudson Valley visit, then definitely put FDR's site and the Vanderbilt Mansion on the must-see list. The FDR museum completed a multi-million-dollar renovation in mid-2013 and it's certainly worth a visit if there's time.

Too many options! I really do like the look of Hyde Park and the places there too.....

I would just do up Vanderbilt/Hyde Park/the FDR sites, have lunch at the CIA, then head back - if you just have one day. It will be a long day, though. The FDR library offers a two day pass which we took advantage of - we split our visit.

You can do one or the other, doing both what I mentioned plus the Kykuit etc would be too much.

On the other hand, Kykuit and Storm King are closer to NYC - White Plains would be a 20 minute drive IIRC.

There is a small church near Tarrytown which has Marc Chagall stained glass windows. Also Matisse. The Rockefellers commissioned them.

Nothing wrong with a 1 day visit to just the Hyde Park area. I would add in the Walkway over the Hudson in Poughkeepsie to Mansions/CIA. It's an 1880's RR bridge high over the river. After sitting idle for 20+ years it was converted into a pedestrian walkway 3 years ago. You can go part way or all the way across.

www.walkway.org

If that is your plan then to keep things simple I'd just take the train to Poughkeepsie. An express train will take about 90min.

I used to live in the area so never tried to rent a car, so I don't know how much of a pain waiting for Enterprise would be. A quicker option would be to take a taxi from the POK train station to Enterprise or Hertz or Avis.

The church mentioned above is in the small village of Pocantico Hill (adjacent to Tarrytown). It also happens to be the same village where Kykuit is located, though your visit there actually starts in Sleepy Hollow, another village adjacent to Tarrytown.

It seems that it all boils to two making a choice between two options for the day:

1. Kykuit and Storm King
2. The Hyde Park sites

You can't go wrong with either. And either can be completed in one day.

They only allow you into Kykuit if you can pronounce it.

Yes it all boils down to choosing between one of the two options, which was the question I asked in my OP.

Is it pronounced Ky-kew-it?

It's pronounced "Ki-cout." (The "cou" in the second syllable is like the "cou" in the word "could.")