I have a 6 hr layover in London.

You can the Acton Mainline from T2/T3 to the Liverpool station direct for about $25. That dumps you near the Tower of London. That's about 40m, a cab will probably take 45 depending on the time.

Assuming your flights are on time:

45 minutes to deboard, traverse LHR and clear customs
30 minutes to get to London
30 minutes to get back to LHR

If you are switching airlines (guessing T3 to T5 with a switch from AA to BA or something similar) factor in 30 minutes to go from terminal to terminal to drop your bags

30 minutes to drop your bag
30 minutes to clear security

So you probably have ~2-2.5 hours to explore.

Tower of London and Tower bridge are just off the Tower Hill station.

Are you wanting to see Westminster Cathedral or Westminster Abbey? Cathedral is near Victoria station a bit closer to Buckingham and Abbey is near St. James park but also next to Big Ben and Westminster.

I misread. We booked both flights on the same ticket so we shouldn't have to recheck the luggage. But a 40 min one way trip on the tube is cutting it tight. But YOLO.

I would go to Windsor instead. Much closer to Heathrow - 20 minute cab ride. Windsor has plenty to keep you busy for a few hours

Haven't been in years, but man, that seems unrealistic. A six-hour layover at Heathrow isn't enough for sightseeing highlights like the Tower of London or Westminster, especially with terminal changes, re-checking bags, and security. Expect to lose 1.5–2 hours on immigration and baggage procedures, and you need to return to your gate two hours before departure—leaving at most two free hours.

So, at best, if all goes well, you might have about 60–90 minutes of actual sightseeing. Maybe Windsor could be doable? 15–20 minutes from Heathrow by taxi maybe.

I'd just find a premium Lounge and drink. Or see if I could get an overnight layover if seeing the city is that much of interest.

Lounges

quote:

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45 minutes to deboard, traverse LHR and clear customs
30 minutes to get to London
30 minutes to get back to LHR

If you are switching airlines (guessing T3 to T5 with a switch from AA to BA or something similar) factor in 30 minutes to go from terminal to terminal to drop your bags

30 minutes to drop your bag
30 minutes to clear security

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I feel like those times are at the very minimum you could hope for.

I get anxiety just thinking about trying to pull off what OP is thinking about.

We got stuck on the train directly under Heathrow for our flight back to the US for about 45 minutes...we were about 250 feet from the platform but just sat there. Airport was a shitshow. Had to get bussed to the massive plane that was out on the tarmac and were the last couple people to board.

My bad. I didn't give enough info. We are coming from Dublin, layover in London while flying back to the U.S. We won't have to go through customs in London. I wasn't sure it would be doable but was hoping. Thanks for input.

With checked bags and a self-transfer, I'd still stay at Heathrow. Have a meal, walk the terminals, or relax in a lounge as noted. You’ll avoid a very expensive missed-flight scenario.

No way I would leave the airport with this layover

That is VERY ambitious to see all that. Maybe one or the other. Tower of London takes a while to see properly. Westminster and that area could be seen in a couple of hours. Depends on the lines to get in both of those. I’ve waited in line at Westminster several times.