Louise Ballard, who grew up in Portsmouth, is going to be walking from Abergavenny in Wales to Gunwharf Quays to raise money for Endometriosis UK and Mind.
Louise, who's 44, suffers from Endometriosis which left her unable to walk for more than a few minutes before undergoing major surgery last year.
She's spent the last 12 months getting fit to take on the 123 mile walk to raise money for two charities close to her heart.
Endometriosis is a chronic illness where the tissue which normally lines the uterus grows elsewhere in the body.
Louise said: "I am excited and nervous to be walking all the way from Wales back home to Portsmouth in aid of Endometriosis UK and Mind.
"I want to raise awareness of Endometriosis,
"Despite 1 in 10 women suffering with this often unbearable condition, many people have never heard of it before.
"That needs to change.
"A year ago, my endometriosis had reached Stage 4 and on a good day I couldn't walk for more than a few minutes before I was too exhausted to go on.
"The chronic pain also took its toll on my mental health.
"Endometriosis and any other chronic illness can have a huge impact on your mental health and that is one of the reasons why the second charity I am raising money for is Mind.
"It's shocking to think that every year, 1 in 4 of us experiences some kind of mental health problem and we need to be able to talk about it openly."
Louise told us why this challenge is so important to her:
She added: "This is without a doubt the toughest physical and mental challenge of my life.
"I'll be walking more than a marathon every single day.
"But knowing the money I raise will be used to fund the vital work that these two amazing charities do is just fantastic."
Louis is hoping to complete the 123 miles in 4 days and therefore is aiming to raise £1234 for each charity.
You can follow Louise's journey or make a donation on her website.