TUMBL×HARD AND SMART
Sunday 13 December 2026 · London Fields Lido

100×100

The Christmas one

One hundred 100m reps back to back, which is 10km. We're doing it outdoors in a heated 50m pool in the middle of December and there'll be lots of mince pies to get us through. There are twenty spots, ten in each lane. Santa hats encouraged. 🎅

When
Sun 13 Dec, 9am
Where
London Fields Lido
Price
£35
Spots
20
Register your interest
10km
Marathon distance
100
Reps of 100m
200
Lengths
2
Lanes, two paces
The set

It's 10km, one hundred metres at a time.

You swim 100m and then you go again, a hundred times over. That comes to 10km, or 200 lengths of the 50m pool at London Fields.

It all runs on a turnaround. Depending on your lane you'll set off approx. every 1:50 or every 2:10. Whatever time you swim and what's left between the turnaround time is the rest you'll get. Swim a bit quicker and you get a bit longer at the wall.

We did this in Brighton in August and all nine of us got to 100. This time it's December and the water will be warmer than the air. There's a second lane too, as we want to give more people the chance to do a Christmas challenge.

Two lanes

Pick the pace that suits you.

There are two lanes running on different turnarounds, so you can pick the one that fits how you swim. There are ten spots in each.

Lane 1 · Intermediate to advanced
approx. 1:50
Send-off for each 100
Comfortable at
1:30 to 1:40 per 100
Set runs about
3 hours

Go for this lane if you've held that pace over a long set before or are a confident and experienced swimmer.

Lane 2 · Beginner to intermediate
approx. 2:10
Send-off for each 100
Comfortable at
1:55 to 2:05 per 100
Set runs about
3 hours 40

This is a good lane for a first 10km and for anyone who wants to get through the whole set still feeling strong.

Not sure which lane? Email hello@tumblswim.com and we'll work it out with you. Be honest about your pace, because three hours is a long time if you've picked the wrong lane. You can always move on the day too.

The morning

A heated outdoor pool in the middle of December.

London Fields is a heated 50m outdoor pool, so this is a proper open air swim in December. Meet on poolside at 8.45am (weather dependent!) for a warm-up and we'll be in the water for 9am. Both lanes will be finished and out by 1pm.

Bring warm layers and something to eat for the feed stops, because you cool down fast standing on a poolside at this time of year.

Twenty spots

Get your name down.

Fill in the form to let us know you're interested. We'll email with further details before the end of September.

Register your interest

It's £35 for the morning. Nothing to pay when you register, and we'll send you payment details once your spot is confirmed.