Flying into Heathrow Airport on a Monday in October around 11 am and departing from Heathrow airport the same day around 7 pm with a group of about 7 people. Want to know if it is possible to exit the airport to see 1 or 2 sights, eat somewhere and check back in, in that short amnount of time.

Do we need to leave time for customs on either our arrival or departure or for airport procedures?

What type of transportation would be best to take from the airport to the 1 or 2 sights and back?

What type of time is involved in exiting the airport, re-entering the airport and in being transported to downtown London and back?

What 1 or 2 sights would you recommend?

Do the bus upper levels have someone talking about the sights we are passing or include a tour?

Would there be a place you would recommend to eat? Maybe an outdoor cafe or another point of interest?

Would we only have enough time to see 1 sight or eat and return back to the airport?

What kind of clothing should we wear in October during this time of day in London?

Thanks for your input.

Just a few short comments:

- In Oct you most likey will not be eating outside

- landing at 1100 does not mean much - you have to get to a gate, exit the plane, walk a looooongway and go through immigration (could be a short line or a VERY long one). So by the time you are ready to head into London it will be noon - 12:30-ish. Then getting to any major site will take about 60 minutes

(you can take a fast train to London but then have to take some other slower transport to get anywhere, or you can take the slower tube right to wherever you want - so either way count on about an hour.)

So now it is already 1:30 p.m. You should be back at LHR by 5:00 p.m. at the latest and since it will take you an hour to get back to the airport you realistically have from about 1:45 - 3:45 free time. Is that worth it - 2+ hours of sightseeing out of your 8 hours?

And w/ a group of 7 in tow - things will not go like clock work.

I would probably recommend taking about 3 or 4 hours at Windsor. Windsor id quite close to LHR and you can get there in 30 mins by bus, less by taxi. Windsor has teh Castle, nice restaurants, the river etc . . . . .

Oh - started out short comments - but then I got on a roll

First, you need to see if your luggages will be checked through.
Immigration queue should not be too bad at that time in the morning (the worst time being early morning with lots of overnight intercontinental flights). I would give at least 1-1.5 hours from de-planing to customs. This could be 2 hours, if you have to wait for EVERYONE's luggages.
On the way back, you need to arrive 60-90minutes before the departure--expect similar procedure to the US airport, including security check.
Healthrow Express runs every 15 minutes and takes 15 minutes to Paddington. If it is after 1pm, you can get a discounted day return fare (London Visit for £16), while the regular return fare is £27 per person. Or you can get carnet--12 tix for the price of 11 and split among 6 of you. It's not the cheapest way to get to London, but it is the fastest--time or money, the choice is yours.
Overall, you'll probably have no more than 4 hours in central London. The Heathrow Express arrives/departs from Paddington, so you might want to choose the destination with easy access from Paddington.

Hard to recommend specific places to visit, not knowing the composition or interests of your group. Maybe you can be a little more specific in what you are interested--visiting historic sights, parks, museums, etc?
Regular double-decker buses do not have guides. You're thinking of hop-on, hop-off tourist buses, but probably not worth given limited time you have. Given central London traffic, tube would be much faster mode of transportation.

Agree October will probably a tad chilly to eat outside. Clothing--just average autumn clothes, maybe a jacket or pullover as it would be chilly, but you won't need winter wool coat or gloves.

I agree that 8 hours is marginal, at best, once you subtract airport logistical time (both arriving and departing).

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