‘I took a ride on the secret abandoned London Underground train the Royal Mail used to deliver mail and it was spooky’ – Tilly Alexander

Located 70ft below ground, the Mail Rail is accessed from Phoenix Place, in a separate building from the bulk of The Postal Museum. The latter is an 11 minute walk from Chancery Lane tube station and where Google Maps will actually direct you. Turning into the street after a series of residential roads, you could easily assume you’ve made a wrong turn, as there’s very little signage – just a small blue sign right outside the metal gate. (Post Office red, surely, would be a more appropriate choice.)

As the sign and staff selling tickets inside explain, you’ll find the entrance for the secret railway line further up the street, hidden behind construction work and a set of temporary traffic lights.This time, the massive ‘MAIL RAIL’ emblazoned on the front signals you’re in the right place. Despite the signs stating ‘Pre-booked entry only’, you can also pick up walk-in tickets (£1 more than the online price).

From here it’s a set of stairs down, left turn and there it is: the Mail Rail depot. I approached the platform, excited to see a train sitting there waiting for me. Its mix of mid-green mini metal doors and curved plastic windows – which could be fastened into a half-circle, turning each carriage into distinct capsules – struck me as half children’s heritage rail, half Tube. The dinky size was definitely more miniature railway, though.

There was no queue and I was let through immediately, ducking my head as I clambered into one of the tiny carriages after reluctantly stowing my bag. The bubble was closed behind me. A few minutes later, my ride rumbled to life and we departed on our 14-minute loop beneath Mount Pleasant, no other passengers on board.

Everything I’d noticed about the platform – earthy yet metallic smell, cool, slightly damp air and background hum – intensified as we rolled down the track into the tunnel’s entrance. Narrow, cave-like passageways lined with wires and what looked like stalactites but may have been dangling roots opened up. So this was what the inside of a Tube tunnel would look like if you could see it, I thought.

We continued up the track, an overhead audio explaining what we were going past. Here was a second tunnel towards Liverpool Street, there a train graveyard for disused trains, here a platform where Royal Mail workers would’ve had 60 seconds to unload.

As we stopped to watch a nostalgic short clip about the Mail Rail through the ages, survey an abandoned platform and experience a power cut in the tunnel (simulated, thankfully), I felt as if I was on a gently thrilling, only slightly spooky roller coaster heading through a mountain. And actually, as with a theme park ride, you can ride this train again and again, since tickets are valid for a year.

But the second platform now crossed, we were nearing the end of the circuit and soon began to climb back up into the comparatively bright depot. My time on Royal Mail’s abandoned mail train had come to an end.

Luckily, though, plenty of quirky Post Office trivia, memorabilia and interactive games awaited transport-loving kids and adults in The Postal Museum’s remaining exhibits – fun fact, the postboxes used to be green instead of red – and gifts shops. I gave in and purchased a salt and pepper set shaped like a postbox and telephone box (£8).

The Postal Museum is open from Wednesday to Sunday, 10am to 5pm, plus some additional Tuesdays in July and August. Tickets cost from £16 for adults, £11 for young people or £9 for children, with other concessions available. Visitors on the Mail Rail must be able to walk unaided for 100 metres and up 70 steep steps, however, for those unable there is also an accessible Mail Rail film shown on the lower ground floor. More information or to book here .