It's an emotional step forward in a near-nine year saga. Today, Pike River family members will travel the furthest into the West Coast mine's drift they have ever been.
The journey to the 170m seal will be the last chance for families to enter the drift before full recovery of the 2.3km tunnel begins.
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Sonya Rockhouse's son Ben was one of the 29 men who died in the blast on November 19, 2010.
It's a very significant step, she said.
"It's like breaking down the Berlin Wall in a way.
"They walked up there to go to work every day - so it'll feel like we're taking the same route."
Her other son, Daniel, survived the blast and today will be the first time he returns to the site.
"Just thinking about one son up there and one son left to deal with the fallout of it all. It's going to be emotional," Sonya Rockhouse said.
"The last time he was in there, he almost died. So it'll be really strange for him."
Rockhouse says it'll be the first time Russell Smith returns as well, the only other man who came out of the mine alive that day.
Another name synonymous with the Pike families' fight for justice is Anna Osborne, who lost her husband, Milton, in the explosion.
For her, today feels like it has been a race against time.
She's been battling Hodgkin's lymphoma cancer for years. Without a bone marrow transplant doctors have given her months to a year to live.
Osborne says the Pike River Recovery Agency worked hard to make sure she can take part in today's milestone, before she goes to Christchurch tomorrow for stem-cell treatment.
"Life is too short, I know that. I had my husband taken away from me," she said, "Yes, I've been thrown cancer - but, Pike has made me stronger, it's made me a fighter.
"If I don't make it, I know I'll be with Milt again. But, I really want to be here for my children and my grandchildren."
The agency said it's given all relevant documentation to WorkSafe and is awaiting its approval before removing the 170m barrier and continuing forward.