Hanoi (CNN) — I'm standing in a dark, large room in Hanoi's Hoa Lo Prison, where Vietnamese prisoners were once held by the French.

Lily Nguyen, my tour guide for the morning, explains in great detail the horrific conditions inside the infamous former prison, which held both male and female political prisoners -- including the guillotine room with its gruesome original equipment still in place.

Mental strength was key for these prisoners, she says, as they plotted and planned escapes from within these gloomy walls. It's a sobering look at the brutal impact of French rule in Vietnam (1887-1954).

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"We were dominated by the Chinese for 1,000 years, then the French and then the Americans," says Nguyen. "But we are resilient, we resist and we never give in," she adds with a smile.

Nguyen isn't a professional tour guide. She's a member of eBuddies , a Hanoi group set up in 2013 to offer free tours led by volunteer student guides aiming to improve their English. Tourists pay only for expenses such as transport, entrance fees or food and drink. When converted from Vietnamese currency, the dong, this usually amounts to only a few dollars.

Tai chi and lucky turtles

Our next destination is Hoan Kiem Lake, a central point in the city to which all Hanoi residents seem to gravitate. In the morning, tai chi is practiced here. But at midday, when we arrive, it's filled with families enjoying the sunshine, teenage couples deep in conversation sitting on lake-side benches and some tourists with their cameras out.

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We make our way onto the red arched Huc Bridge, stopping in the middle to chat. According to legend, explains Nguyen, a divine sword was sent to Emperor Ly Thai To in order to defeat the Chinese. When they were finally expelled from the country, the ruler made a visit to the lake, where a giant golden turtle took the sword in his mouth and disappeared into the water, returning the weapon to the gods.

"It's very good luck if you see a turtle here in the lake," says Nguyen. "But I never have."

Nguyen links her arm through mine, and we begin to circle the lake.

"The water here is very calming" she says. "Whenever I am feeling stressed or worried, I come here and sit by the lake and I feel better."

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Like traveling with a friend

Stopping at a small juice bar, we take a break from walking and share photos from our phones while talking about our families, religion, Brexit and football.

Occasionally, I use a word Nguyen is unfamiliar with and she looks it up on a translator app, but her English is good. Her enthusiasm is infectious, making the tour feel more like a day out discovering the sights with a friend. We step back out into the heat and walk around the corner to St Joseph's Cathedral.

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Built by the French and inaugurated in 1886, it's the oldest church in Hanoi. With twin bell towers, it's reminiscent of the façade of Paris' Notre-Dame Cathedral. Making our way into Hanoi's Old Town, the streets become narrower and more congested with motorbikes and street vendors.

Despite the fact that I'm taller and older than her, Nguyen takes my arm protectively and leads me through the crowds, walking into the street first and holding her arm out to indicate to traffic to slow for us to cross. Returning to my hotel I notice my half-day tour has run over by two hours, but my tour guide for the day was happy to extend the time. We hug goodbye, and Nguyen makes a dash for her bus home.