It's in a quiet part of town about 10-15 minutes from several museums including the Natural History Museum. As previous posters mentioned, Earl's Court tube station is only 5 minute walk from property to get you around the rest of the city. Took a 55-minute ride on Piccadilly line from Heathrow to hotel for only 2.10 GBP. The Cromwell Hospital bus stop is right outside the Kensington Marriott, so another great option for traveling.
I booked a Queen Deluxe room and was upgraded to a Family Room (2 Queen beds) using Suite Night Awards. I did get Exec Lounge access / free breakfast as a titanium. As others have mentioned, the Executive Lounge is pretty dreary and not well maintained. They are serving breakfast (6:30am - 10:30am weekdays / 7am - 11am weekends) and hors d'oeuvres in the evening upstairs in the restaurant. The breakfast is decent (far from amazing) with a selection of pastries, cheeses, meats, fruits, yogurts, cereals, and hot items. Eggs and pancakes are available to order on-demand. Outside of the free alcohol, the hors d'oeuvres in the evening were pretty limited. Lots of mini-salads.
Staff is nice and helpful. Rooms are good. Lounge / breakfast is average.
This is the dreary executive lounge. Very few snacks throughout the day. Bottled drinks don't get restocked very often either.
