Rylan Clark-Neal is joined by stars of reality TV to explore London's largely disused Post Office Railway which runs 70 feet beneath the city's streets.
| Name | Type | Role | |
|---|---|---|---|
| Rylan Clark | Guest Star | ||
| Ashley Buckenham | Guest Star | ||
| Gabby Allen | Guest Star | ||
| Charlotte Dawson | Guest Star | ||
| Marcel Somerville | Guest Star | ||
| Alex Gibbs | Guest Star | ||
| Richard Merritt | Director |