My first apartment in Amsterdam had normal windows and long balconies so cleaning the windows was as simple as a bucket and sponge on a sunny day. Then I moved to the historic area of Amsterdam where it’s all sash windows which slide up to open, obscuring part of the glass so they’re impossible to clean yourself.
The answer is simple; window cleaners.
One morning I opened the curtains of my room one morning at sleepy 7am to come face to face with a man on a ladder with a sponge in his hand; the window cleaner. Teams of them with ladders of different heights loaded on old-fashioned looking carts come by about once a month. They’re paid in cash which is why they’re around first thing in the morning.
This is not a job for the faint-hearted, the apartments are 5 storeys high and you’ll need to climb and stretch, you’ll need good balance, and while it’s not a job for a rainy day you’ll be working winters.