My family and I will have a 23 hours layover in IAD in November prior to flying to FRA. We will arrive at 7pm and will depart the next day at 6pm. Any ideas or recommendations how to spent the layover in IAD or preferably Washington downtown? What's the best way to go into downtown and how to spent the day there? When should we go back to the airport to make it to the international flight?

Thanks for any recommendation

Do not spent 23 hours at the airport.
Suggest you try Google or some other search engine for "what do in DC in November" or "top 5 things to do in DC" or combination thereof ... there is so much readily available information ... if you still have questions, then come back based on your research.
Like any major airport, IAD has myriad transport options ... bus, bus and metro, taxi, Uber, Lyft etc, Limo ... "best" is a relative term based on how many traveling, budget, any mobility issues, luggage (or lack thereof) etc ...
Be back at the airport, three hours before your departing flight.

Are you flying in on a weekday or a weekend?

With family and luggage in tow, the simplest option is probably Lyft/Uber to and from wherever you're staying in the city (~$50 one way). Otherwise, the bus-to-subway transfer is inexpensive, though can be flaky and time consuming; doubly so on weekends.

Here are some options, given your timetable:

• If you're interested in museums on the mall, most of them will have long lines -- pick one and go early. Alternately, you can walk the length of the mall for touristy photo-ops (US Capitol -> Washington Monument -> White House -> Lincoln Memorial -> Kennedy Center).
• With small children, visit the zoo! It shouldn't be too crowded, except for maybe the panda enclosure ... Dress appropriately for the weather, and then stop by Nando's or Open City in Woodley Park afterwards.
• If you're a horror movie buff, visit Georgetown and see the Exorcist Steps, do some (horribly overpriced) shopping, then stop by Baked and Wired for coffee and cupcakes.
• For something more local, try visiting some stuff in residential neighborhoods (e.g. Eastern Market) or consider skipping DC altogether and visiting Old Town Alexandria.

When you head back to the airport depends on day and means of transportation. In general, I'd again recommend Lyft/Uber for simplicity -- plan to leave the city around 3:00pm to arrive at Dulles by 4:00pm (~2hrs. before your flight). Budget more time if going by subway to account for transfer(s).

I'm sure somebody here will find something to disagree with me about.

^ I'll disagree that lines are likely to be long at the museums in November. If it's a weekday, probably no lines. Weekend, maybe short lines except Air and Space. November isn't high tourist season! But otherwise lots of good ideas.

Also, a popular spot for airplane buffs is the Udvar-Hazy Air and Space museum, which is near Dulles Airport. You could go there after lunch and then you're quite near the airport. Also, I don't think you need 3 hours early at the airport, unless you typically need extra time. I usually leave less than 2, but do have pre-check and know my way around. 2.5 should be adequate. If you do go to Udvar-Hazy first you also avoid the traffic risk of leaving mid-afternoon, which sometimes things can get busy.

Question about transit into DC, I have to wait for my friend at IAD on friday morning for 5 hours( if both flights come in on time) so hoping to kill time at one of the lounges.Friend gets in around noon, looking for a cheap and easy way to get into DC, were staying at the marriott georgetown

Hmm, November is prime school group season ... or at least, every time I can recall going during a school trip was something in that timeframe anyway. I haven't done the museum circuit in a while though, so I could see it being low traffic as well.

I'm assuming you're arriving from a domestic flight -- I've never tried entering a lounge after having flown, though they may let you in? I hear the TK lounge is nice, and you should be able to get in with UA Gold. If I were you though, and since you have time: hop on the Silver Line Bus ($5 cash/credit) then transfer to Metro, get off at Reston and take the DC Circulator bus towards Dupont Circle (~$1, might be a discount for the Metro transfer). It should drop you off in the middle of Georgetown. Should take probably 45 minutes to an hour, traffic permitting.

Yes I am arriving on a domestic flight from EWR, so most likely in C concourse, my friend is arriving in A I believe on a cr2 from ROC. Thats what I was thinking to TK lounge is between my PP or *G I should be able to get access to it upon arrival. On loungebuddy app it does not say anything on it for any of the PP lounges that I have to be a departing pax. If TK doesnt work, then I will start my way to the others and hope one will work.

Thanks for the advice and I will most likely take that routing as it seems fairly easy and cheap to do. I will check out lyft and uber as well to see if any discounts make it any cheaper then the $40 people are saying it is. I have plenty of time since as of now the hotel said they only have queen beds available and I booked a king but hoping for an upgrade to a bigger room or suite upon checkin.

Knowing your budget is always helpful to answer questions such as this. But, presuming that you are on a moderate budget, plan on an Uber or UberXL if enough people and bags and plan on 2 hours into DC from the time you arrive at IAD to get your bags and make it to your hotel. I would stay somewhere near the Mall such as the JW Marriott and plan a couple of specific activities such as 1-2 of the Smithsonians. Everything easily walkable. With a 6:00 PM international departure, I would depart DC at 3:00 PM, be at IAD no later than 4 PM and in good shape for a 6:00 PM flight.

I believe the Georgetown Marriott is actually closer to GWU or Dupont Circle (in terms of public transport). Siliver Line Bus to Metro to Circulator bus toward Dupont Circle would still work (I think it's at the Rosslyn station though), but stay on past Georgetown until M & New Hampshire NW, which is right around the corner from the Marriott.

Alternatively I think a slightly faster way is to do Silver Line Bus to Metro and get off at the GWU stop, and walk ~10 minutes to the hotel, but this might be harder if you have a lot of baggage.

Its pretty close to dupont circle from what I have seen on the maps. I haven't been to dc in years. We each should only have a roller bag and a back pack so it wouldn't be too hard considering we just did a bunch of walking in thailand recently but I had to carry the bags since my friend couldn't carry her bag because of her sunburn so it was a nice walk in Koh Phi Phi from the ferry to the room with two bags strapped to me.

*G requires a departing flight. Not sure about PP.

Unless there is some strong reason to wait for your friend*, you'll probably both be better off paying for separate Uber/Lyfts allowing you to enjoy your time in DC for a bit longer.

*better be a fiancee/spouse/boy-girlfriend or grandparent who doesn't speak English

22nd and M is what I would call "West end"; not Georgetown.

Ended up being able to get in the TK lounge with my PP, even though I had my *g card ready as a back up. No questions asked and stayed for a few hours.
They even remembered me when I came back a few days later. She's one of my best friends and we travel a lot together but she has not done much by herself. Went to g meet her at the gate but it was blocked from near the smoking lounges all the way to the small A gates for 20 minutes because someone left a bag and the dog alerted on it.

According to Marriott she was my wife, when they left us a note in the room with a bottle of wine and a cheese/meat board since they room they upgraded me to would not open with 4 keys from the desk and the master keys from housekeeping and security. Got downgraded one night and the next two nights the moved us to a big suite.