Just west of Baltimore’s Penn Station, trains crawl into a stone-arched hole, then creep through a dark passage. Small lights punctuating the walls are all passengers can see of the Baltimore and Potomac Tunnel — but plenty hides in the shadows.

Riders can’t see the chipped concrete that reveals patches of the original brown bricks used to form the tunnel arch just after the Civil War; the water that pools and trickles between the steel tracks; the mud between the wooden beams; the smooth hunks of ice that cling to the walls and encase telecommunications conduits like contorted claws.

If not for the presence of Amtrak maintenance workers making some routine repairs, walking the B&P Tunnel could feel like a scene from HBO’s post-apocalyptic series “The Last of Us.”

Passengers are perfectly safe as their trains navigate the 1.4-mile tunnel — 150 trains do it everyday, according to Amtrak officials. But the darkness hides many of the reasons the narrow, curvy passage so desperately needs to be replaced.

The replacement that’s underway — an estimated $6 billion endeavor named for Baltimore civil rights icon Frederick Douglass — already has faced a community push to derail it. Now it has to survive a president hellbent on clawing back the promises of his predecessor, former President Joe Biden, a man who just so happened to love Amtrak — so much so that he came to Baltimore to celebrate the tunnel getting built.

Billions in federal grants followed. A large U.S. flag hung by the podium that day is now mounted in an Amtrak maintenance facility a stone’s throw from the eastern opening of the tunnel. Amtrak workers still look at photos of that day.

Standing just outside the tunnel on a cold January night, Luigi Rosa, an Amtrak vice president leading the passenger-rail company’s team working on the new tunnel, said it’s sometimes hard to believe that the railroad still depends on a piece of infrastructure built when Ulysses S. Grant was president.

“This is the worst bottleneck along the Northeast Corridor that is the busiest railroad in North America,” Rosa said.

To step into it is to step back in time, yet keep the present within earshot.

The tunnel was designed when most streetcars were pulled by horses and trains spewed coal smoke. High-speed rail was nothing more than a dream. The result is a tunnel with a curvature that limits trains to 30 mph.

Graffiti marks some sections of the 150-year-old walls. Trash, debris, even a still-good ticket for a MARC train ride, litter the track area. Branches, too, having fallen through one of two midsection cuts in the tunnel that exposes it to the open sky — a primitive way of venting the locomotives’ exhaust.

Safety standards were different back then. The tunnel can’t accommodate modern fire and safety equipment. Small nooks cut a couple of feet into the tunnel walls every 100 feet or so allowed rail workers to jump in as trains rumbled past mere feet away.

Today, the nooks are a relic. When work on one of two parallel tracks is needed, crews shut down the entire tunnel.

The new Frederick Douglass Tunnel, once built, will alleviate these issues.

Amtrak plans to bore two tunnel tubes underneath West Baltimore in the coming years with gentler curves that trains can speed through at up to 100 mph. When a track needs maintenance, one tunnel tube can keep train traffic going while the other closes. The master plan includes four tunnel tubes, but many officials doubt that numbers three and four will get funded in their lifetimes.

The chosen route for the new tunnel sidesteps the current one, which passes under mostly white Bolton Hill and largely Black neighborhoods such as Madison Park and Sandtown-Winchester. The decision has some in the neighborhoods up in arms.

Those communities have decried the plans in public meetings, citing everything from air quality concerns, the threat of construction fallout, and a possible future of freight trains hauling hazardous materials under their homes. They lodged a formal civil rights complaint, arguing other routes were available that wouldn’t cause as disproportionate harm to majority Black neighborhoods.

Construction crews already have started moving utility lines and performing other prep work. It will be a couple of years before a tunnel boring machine — currently being manufactured in Germany — starts eating through dirt and rock. And years beyond that before the new tunnel opens.

Meanwhile, Amtrak crews diligently keep their B&P Tunnel functional.

“It’s showing its age, but it’s safe for our customers and our passengers and we maintain it to that point constantly,” said Dante DeAnnuntis, Amtrak’s director of integration and operations on the Capital Delivery side of its operations.

Water is a huge issue. It seeps into the tunnel on all sides.

“We’re constantly working to divert the water or pump it out,” DeAnnuntis said.

It’s most obvious in the dead of winter. In the tunnel’s deepest sections, water can freeze into plots of ice inside the rails. Trains have no issue passing over it, but DeAnnuntis and his crews worry about the catenary wires above that power the electric trains. They run “ice patrols” to chip away the dangling icicles.

Fear has spread since Trump took office that federal spending would be frozen. He’s closed the U.S. Agency for International Development and ordered a pause in grants and loans. He’s gone after the landmark bipartisan infrastructure bill that funded Amtrak modernization projects up and down the East Coast, including the tunnel, named for the Black reformer and abolitionist who lived in Baltimore. (Trump also has shut down the federal government’s diversity, equity and inclusion efforts.)

The tunnel work bores onward, though, the product of both timing and necessity.

DaAnnuntis said it’s an “exciting” time to work for Amtrak with all the ongoing projects. Rosa called it a “once-in-a-generation opportunity for Baltimore and the railroad.”

Until then, trains bound to and from Baltimore still slide slowly through a tunnel of generations past.