This Sunday, 28 April, around 40,000 people will run the 39th London Marathon.
For many, it'll be their first time.
These are the 10 things which every London Marathon virgin will want to know.
1. Toilet queues
Greenwich Park and Blackheath are lovely settings for the start.
You won't really enjoy them - you'll be in the queue for the toilet.
And that last safety wee won't make a difference anyway because as soon as you're in that starting pen, you'll want to go again.
2. The starting pen
Wherever you're directed to start, choose your friends wisely.
You're stuck with these people for at least the first mile.
3. Fancy dress
However good the cause might be, fancy dress is not as funny as you thought.
This emotion will kick in around mile eight when a 10ft gorilla jogs past you.
The same goes for the free energy gels - the novelty wears off quickly.
It's not all Big Ben and Canary Wharf. Ever seen Isle of Dogs Asda or Surrey Quays station from the outside?
Get ready to tick them off the bucket list.
The roar of that crowd around Cutty Sark as you go from mile six to mile seven is the most reassuring thing you'll ever hear.
There will be thousands of people there - they'll make you smile, they'll probably make you speed up.
Don't forget there are still 20 miles to go though.
6. The halfway point
Your run towards the 13-mile mark will be one of your highlights.
Going across Tower Bridge with thousands of people either side of you will be enough to bring a tear to your eye.
The hard bit comes next. As you head up Shadwell Highway, DON'T look to your left. Trust us, don't. (There are people running the other way to you, fast).
7. The drinkers
People use your marathon to start drinking very early. A 10am lager is nice for them. It's nice for the pubs making a killing. You'll be livid.
8. The name thing
You've got your own name plastered across your chest, mainly because it's what everyone else does.
Around the streets of Charlton, Woolwich and Greenwich, hearing complete strangers yelling your name will be a nice thing.
By the time you get to Canary Wharf, it'll be weird and annoying.
9. Canary Wharf
People do go there at the weekend after all and, after a lull in the crowd around the Isle of Dogs (keep your biggest tunes for that bit), the sound of the crowds at Canary Wharf will be one of the best feelings of the day.
10. The last bit and the end
Everything you've ever been told about sweets and strangers goes out of the window here. You'll take anything.
The roar of the crowd is getting louder as the Mall is getting closer.
But that bit from Big Ben to the finish line will feel like it's a marathon of its own (it's not, it's only a mile, keep going).
There's a goodie bag at the end but don't get too excited.
As soon as you cross the line, you'll crave sugar, chips, beer - all kinds of things.
What you're probably not after is a carrier bag containing numerous leaflets, a slightly odd cereal bar and a complimentary T-shirt.
Oh, and on that beer - it'll taste weird. It'll get better but that first one will taste weird (and crying at the finish line is absolutely fine - you've just had one of the best days of your life.)
A version of this article originally appeared on Newsbeat on 20 April 2016.