Day trip from Amsterdam

This may be too far for you, but I'm scheming on going to the Netherlands Open Air Museum. It's covered by the Museumkaart, but probably not by the I Amsterdam card. Last time I was in the Netherlands, I missed going there due to illness, so I'm somewhat obsessed by visiting it next month when I'm in Amsterdam.

I checked Google Maps and Rome2rio for transportation options. There appear to be Intercity trains directly from Amsterdam Centraal to Arnhem Central Station that run at 25 minutes past the hour and take about 1 hr 5 min. The return direct trains appear to leave Arnhem Central Station on the hour and take the same amount of time.

There are public transportation and walking options that take an additional 45+ minutes from Arnhem Central, but I'm inclined to spend the money for a taxi direct between Arnhem Central and the museum to save time and my feet.

I’m a single older female traveling solo and am in Leiden right now, which is a very charming place and which I would recommend for an easy day trip. It’s a 45-50 minute train trip from Amsterdam that costs around 9 Euros each way. The city center is very close to the train station (I walked it in less than 10 minutes). I am really enjoying my trip here today. The architecture is gorgeous and there are museums galore, plus a botanical garden.

If I have time, I may try to make it to Den Haag later this afternoon, which is about 15 minutes from here, but I’m playing it by ear (one of the perks of solo travel). 😊

An easier day trip to an open-air museum is Enkhuizen, 1 hour from Amsterdam Centraal station on a direct half-hourly train. It is a gem of a historical harbour town, and the Zuiderzee Museum has a rich collection of the traditional life in this area. No selfie taking tourist crowds and all very walkable.
Even easier is Haarlem, 20 mins from Amsterdam Centraal with 4 trains per hour. Beautifully situated on the river Spaarne it has two wonderful museums: the Frans Hals Museum and the Teylers Museum. The very city centre is a 10-min walk from the railway station.
If you're into Dutch art, you can't miss The Hague with its wonderful Mauritshuis museum. A 50-min journey from Amsterdam Centraal, with 2 direct trains and 2 involving a change at Leiden (make sure you take the train to »Den Haag Centraal«). The city centre is less than 10 min from the station.

You can, of course, break your return journey from The Hague in Leiden. It's a lovely university town with the largest historical centre after Amsterdam. And why wouldn't you have your dinner there before getting back to the Big City? Direct trains to Amsterdam Centraal run 4 times per hour, taking 35 mins.

Is the Waterland Bus pass still available? For 10€ pp we rode all day. We visited Marken, Volendam and Edam. The bus passed through Broek and Monnickendam which looked quite nice as well. It was easy and convenient, the busses were frequent. You could visit one place or as many as you choose. You set your itinerary. Great value and a great day. Back then, we purchased the pass somewhere behInd Centraal Station. Safe travels and enjoy your visit.

I just spent 6 days in Amsterdam/Haarlem the last week of April. One of those days I took the train from Haarlem, where I stayed, to Delft and spent 3 or so hours there. Wonderful town! With the Olde Kerk, the Nieuwe Kerk. I also did Rick's walking tour and enjoyed it so much. He suggests spending 2 nights in Delft which I would do on a future trip.
Then I hopped back on the train to den Haag and had a delightful time touring the Mauritshuis museum. I was also on my own.
Back in Haarlem, I had dinner at a wonderful Indonesian restaurant. Back to hotel to pack for a flight home the next day!
The others have given you many wonderful suggestions - there are several I would love to try. You can't go wrong in Holland finding interesting things to see and do. Enjoy!

Is the Waterland Bus pass still available?
For its proximity to Amsterdam places like Volendam and Marken can be unpleasantly crowded in this time of year, especially when a couple of tour buses arrive. The same is for the popular Zaansche Schans.
Invest a little time in travelling to a place somewhat further away and your trip will be much more rewarding.

We were near Amsterdam for a longer period this spring and I think we managed to get to all of the suggested day trip places. If it's a smaller city you're wanting, I'd recommend the easy train trip to beautiful Leiden or go further to charming Delft with a stop in Den Haag to see the Mauritshuis Museum. If you want to experience countryside, the 10€ waterland route that goes north of Amsterdam is relaxing and a good way to get around. We liked walking around in Marken more than crowded Volendam, although we loved the little local history museum in Volendam next to the TI.

Lo, I hope you get to the outdoor museum near Arnhem and the wonderful museum with more Van Goghs, in the park. We tackled it the third week we were in the area and used a car to get there. The museum was busier than I'd expected on a weekday afternoon.

Thanks so much for your tips!
So much appreciated!!
Now I have to make a decision :-)

Thanks so much for your tips!
So much appreciated!!
Now I have to make a decision :-)