May 1st in Budapest

Not much will be closed, but it is a celebration time. Some years they have an airshow over the Danube too. Part of Andrassy ut will be closed for the cars. Last year more of a demonstration up and down Andrassy ut than a race. The upper part of Andrassy is generally closed with food booths and concert stages and this can extend all the way to city park. Similar activities on the river front be sure and check out around the north end of Széchenyi tér

Very excellent time to visit Eastern Europe as its a big holiday all over the region.

But yes, most (all?) of the museums will be closed on the 1st of May
Also they are closed on Monday in general
Jewish Budapest shuts down early on Friday for the Sabbath and reopens on Sunday.

See if you can open these pictures. Its a couple of snap shots and a video from May Day 2017 https://1drv.ms/u/s!Ai7Zk-szxfTJhvYKNQfcihV72y4SIA?e=Y6rn5i

I had the great good fortune to be in Budapest for May 1 in 2018 and it was such a fun day--I knew I wanted to check out the events in City Park (Varosliget) so I first visited the zoo which is at the left side of the park, then spent a few hours at the festival going on there--rides, crafts, excellent & cheap food and drink, music--perfect day to just relax and enjoy the wonderful weather. Later in the day I took the M1--it was jam-packed--down to Deak Ferenc ter to see a bit of the auto racing. There are events going on up on Castle Hill so that might also be an option for you if you want to mingle with the locals enjoying a holiday. A day spent on Margit sziget is always wonderful, lots to see and do and I am counting the days--83!!--til I get to see the nesting storks at the little zoo there.

You might check a site that lists events www.welovebudapest.com for more info on what's going on while you're there.

Thank you both for the encouragement to participate in the festivities. I'm getting contradictory answers about Museums. Some places say they will be closed, others that they will be open by law, but free for EU Citizens (which may be so crowded that they may as well be closed?). As Friday will be our last day, we may just wander City Park and other Labor Day Festival sites and walk up to any view points we missed earlier in the week; or we could head out of town to hike (perhaps with one last bath at the end of the day). As we tend to front end load the things that matter most to us, Friday may be a good day to chill.

I checked the National Gallery and it showed being closed on the 1st. The others may vary. Sorry, i haven't been in many, I'm not a big museum hound. Cant help you much. The House of Terror is best done first thing in the morning. Get there 30 minutes before it opens. Beyond that I cant help much, although I love the railroad museum.....

If upon arrival you get a travel card, you will not run out of things to do ... i promise.

Running out of things to do is never our problem. We travel slow, and often stay longer at sights than most people. Also we like small off beat museums.