As front doors go, you probably wouldn't notice it if it wasn't for the ever-present protesters outside. They might prompt you to glance at the sign next to the door and you'd notice the blue plaque on the wall. Then you'd understand.
This is the door to Marie Stopes' historic central London family planning clinic, and it's still providing vital reproductive health services to women and men today.
Those services include abortion, which despite the fact that one in three women will have an abortion in the UK, remains controversial 49 years after the Abortion Act was passed by Parliament. And that's why the protesters are here.
If she'd been alive today, Stopes would no doubt have had strong views on the rights of women to access abortion clinics unhindered, and she'd have challenged the stigma that to this day surrounds women's right to choose whether and when to have children.
Stopes was a family planning pioneer and women's rights campaigner born in 1880. She would certainly be described by some today as a 'difficult woman', by which I mean unafraid to stand up for what she thought was right, and prepared to fight for it.
When it comes to our bodily autonomy, I'm delighted to say there are quite a lot of difficult women - and men - these days. You only have to look at recent political rhetoric and actions to see how desperately they're needed in large parts of the world.
Stopes died in 1958, and by the 1970s, her central London clinic was in trouble. It would have closed had it not been for another family planning pioneer, Dr Tim Black, who bought and turned it around.
From that blue door Black grew a global network of family planning services supporting some of the poorest, most vulnerable women around the world.
But as the charity that bears Marie Stopes' name celebrates its 40th anniversary, can we really say that, here where it all started, women's right to choose has become a reality?
It might not be perfect, but here's the top four on my wish list for women:
1. We're a pro-choice society, but there are still a small yet significant number of people minded to stand outside abortion clinic doors and do whatever it takes to prevent women from having an abortion.
This behaviour wouldn't be tolerated outside any other health service. I'll leave you to decide why it's ok outside abortion clinics. In the meantime, ask your MP for buffer zones to protect women.
2. What about contraception? It's more readily available now and better than ever. There are long-acting methods like the coil, one-off methods like the cap or condom, and those somewhere in the middle like implants or injections.
But men have just two options: the condom or vasectomy, so responsibility for contraception continues to rest with most women. And with the trial for a male contraceptive jab halted early due to 'side effects' that's unlikely to change soon.
Let's continue to invest in new methods of contraception for everyone, and protect the services delivering them.
3. Under-18 conception rates in the UK have been falling thanks to phenomenal efforts to implement Teenage Pregnancy Strategies. It's a huge success, but one that has been achieved despite a continued refusal, by successive governments, to put sex and relationships education on the curriculum.
Imagine what we'd achieve if we gave every young person the skills and knowledge to enjoy healthy, respectful sex lives: fewer sexually transmitted infections; fewer unwanted pregnancies; and much-needed clarity on consent.
Why wouldn't we want that for our children? Bring this up with your MP too.
4. Next year marks the 50th anniversary of the Abortion Act, which was passed thanks to the considerable efforts of women and men who campaigned for safe, free, legal abortion.
This is a reality for women in England, Wales and Scotland, but as this week's appeal at the Supreme Court by a mother and daughter to allow women from Northern Ireland access to NHS-funded abortion care made painfully clear, women there are still subject to one of the most restrictive abortion laws anywhere in the world.
Most of them have no option but to find the money to travel to England, or have a baby. It will take political courage to put this right, but women in Northern Ireland deserve nothing less.
The past 40 years have seen a huge rise in the number of women accessing contraception, with the numbers in the world's poorest countries jumping 30 million in just the last four years. This increase has contributed to a decline in maternal mortality worldwide and progress - still achingly slow - in girls' education.
It's been a phenomenal achievement to get this far, made possible by huge collective efforts and considerable political courage.
And some of this success can be laid, squarely, at that blue door on a quiet central London street, and the difficult pioneers that worked behind it. Here's to the next 40 years.