Hi Missy. #1 Rule: Wear good walking shoes!
Since you have time, go online and review ordering a Metro Pass. I didn't know about this and could have gotten a senior pass, but the 7-day pass I bought upon arrival was still cheaper for the 4.5 days I was there than paying for each ride. And it was definitely quicker. Also, if you use Google Maps on your phone and put in your destination, it will show you which subway lines to take and how long until the next one.
Metropolitan Museum now charges full price for anyone who is not a NY resident or student in one of the cities schools. For me, that was $17, Senior Rate but it's good for 3 consecutive days and for all three of their museums:
Main on 81st
Met Breuer
Cloisters
Museum of Natural History: Go in the back door! And go early. The line was much shorter and there are also computer kiosks to buy your tickets. I spent an hour, walked out the front door at 11:00 and the lines to get in the front entrance went around the block!
The lovely "Woman in God" (formally named Portrait of Adele Blouch-Bauer) by Klimt now resides at the Neue Galerie near the Met. Visually stunning. I have Erin and Richard to thank for this little treat. Also the cafe at ground level was very lovely and tasty. There is a cafe in the basement, but it's just a cafe in the basement.
I have three maps with upper, middle and lower Manhattan. I would try and plot where I was going so I didn't keep crossing town:
High Line down around 14th street was fun to walk. Again, I did this early when it was cooler.
Roosevelt Tram was a nice break.
World Observatory was worth it...again, most people seem to have bought their tickets online...I had to wait in a line for mine while they got to cut ahead.
Be prepared to cry at the Trade Center Memorial. However, the fountains are very peaceful and a lovely tribute.
I was VERY pleased at the number of healthy fast-food spots around midtown...many with giant salads or premade sushi. I'd grab a salad or noodles and sit at one of the city parks. Since I was by myself, I wasn't that interested in restaurants. I did go to Clinton Street for breakfast. It was great.
Oh...you have to see the ceiling at the main Public Library Reading room on the 3rd (?) floor. Then go down to the basement to the Children's library to see the REAL Winnie the Pooh stuffed animal.
On my trip three 2 years ago, I walked across Brooklyn Bridge with Sandra and her friend Heidi. Very iconic, if a bit crowded because there are reserved lanes for bicylists. Then we spent a few hours rambling through Central and had lunch at the Food Court in the basement of The Plaza on 59th.
I had visited the Statue of Libery, Empire State Building, Little Italy and Chinatown years ago.
My midtown hotel charged $25/day destination fee on top of room and taxes Be prepared for that extra hit.