Where do you go on rainy days that isn't softplay or trampolining?

[stillsleeptraining]

I'm dreading 5 months a year of this for years and years! We usually go to the woods, park, cycling etc after swimming.

Ideas appreciated! We're in London

We generally just stay in at home tbh. Usually it doesn’t rain all day so can go outside again after or beforehand.

Sometimes we go shopping (food/ diy/ house stuff/ ikea). If we need new kitchen/ curtains/sofa or something big in house that might require looking around several places over a few months we aim to keep that for winter.
ikea is great, our closest is an hours Drive away, has food, and kids play area in one place, so takes up most the day.

We use raining days at home to bake, paint chores and diy. We have swept garden leaves and cleared gutter this morning, and quick walk with kids bike whilst dry an hour or so. Now Ds is just playing, dh and I measuring up and deciding on new blinds

We also visit friends or invite them over for afternoon tea and cake or mulled wine in winter.

If it's dry - we went outside. Proper boots, even for DD as wellies aren't really good for walking I find.
Stately homes with parks/gardens

If it rains
museum, London has great ones even with toddlers and they are nearly all free
libraries on Saturdays
when a bit older: Kids shows at the cinema
baking
boardgames
movie time at home with snacks
arts and craft (if you have the patience)
meeting with friends for a playdate

Londoner here. We asked for annual passes to the Aquarium and to Tate Modern for Christmas. DC choose route (bus/tube/river boat) and we take sandwiches. We now know lots of the fish/attendants by name!

I'd keep doing all the things you mention in the OP.

We're very much a "get some fresh air" family, even if it's pissing down. Decent waterproof gear is cheaper in the long run than having to pay for activities every weekend because the weather's a bit Ming.

Where in London?

Greenwich is good (big map)
Tate Modern to hare around the Turbine Hall/go to Tate Play
Walk by the river/look for treasure
Mudlarks Gallery
Museum of the Home
Transport Museum (I think one ticket covers a year, or used to)
I'm nowhere near the Science Museum but if I was I think we'd live there
...

I also find an hour out in a muddy garden/puddle with little ones is plenty - come in after, hot chocolate, TV.

We don't do any of the above in enormous depth but we go, stretch our legs a bit, try to take in at least some of what's going on, then head back.

London has loads of activities available! This morning we've been to an art exhibition, and then gone to a big playground as the forecast has improved - equipment is wet but no rain now and we have rain trousers.
In November/December we do lots of theatre shows and concerts. Then there are museums, galleries, places like Discover , role play centres, immersive art shows, touristy stuff like the Aquarium and Shrek. Then more local stuff like libraries, leisure centres, swimming, children's centres, local classes for things like dance and music.

Ds used to love role play and dressing up in one of his many costumes such as Spiderman. We would invariably be part of the story he created! Also loved playing shop with tins etc from the cupboard and us as shoppers. We did play doh, drawing, painting, just playing.

How many years of your life you been hibernating for? This is ridiculous. Do you write a letter to excuse your children for outdoor play\breaks during these months?

Nowhere. I'm in rural Essex, and the traffic is so bad I'm virtually imprisoned in my house. Much of the town is a no-go on Saturdays.

Museums (RAF is our current fave)
Galleries
London zoo (loads of it is indoors - we have annual passes)
Bowling
Cinema (Vue do cheap showings on Saturday)
Swimming
Ice skating
Library
Have friends over (and hopefully it's reciprocated)
Visit family or invite them to visit
Mini golf (probably for older kids)
Lego club (they run a few out of local libraries but there are some private ones, it's aimed at over 5's though)

It's rare for a whole day of heavy rain so go out earlier or later.

We also like an indoor day and have busy schedules in the week so I often use a rainy day as a good excuse for a lazy / pj afternoon.