Here's an ideal itinerary for 3 days in London that excludes museums:

Day 1:

Start your day with a visit to the iconic Tower Bridge. You can walk across the bridge and take in the stunning views of the River Thames. After that, head over to Borough Market, one of the oldest and largest food markets in London. You can sample some delicious street food and pick up some souvenirs. Next, make your way to the famous St. Paul's Cathedral. You can climb to the top of the dome for breathtaking views of the city. End your day with a relaxing stroll along the South Bank, where you can enjoy street performers, live music, and beautiful views of the river.

Day 2:

Begin your day by visiting the Buckingham Palace, the official residence of the British monarch. You can watch the Changing of the Guard ceremony, which takes place daily during the summer months. After that, head over to the nearby Hyde Park, one of the largest parks in London. You can rent a bike or a boat and explore the park at your own pace. In the evening, catch a show at the West End, London's theater district. There are plenty of options to choose from, ranging from musicals to plays.

Day 3:

Start your day by visiting the iconic Big Ben and the Houses of Parliament. You can take a guided tour of the Houses of Parliament and learn about the history of British politics. After that, head over to the nearby Westminster Abbey, a historic church that has been the site of many royal weddings and coronations. Next, make your way to the Camden Market, a vibrant and eclectic market that offers everything from vintage clothing to street food. End your day with a visit to the London Eye, a giant Ferris wheel that offers panoramic views of the city.

I hope this itinerary helps you plan your trip to London!