The world's first mountain-climbing cog railway reached which New Hampshire summit in 1869?

The Mount Washington Cog Railway is the world's first mountain-climbing cog railway (rack-and-pinion railway). The railway is still in operation, climbing Mount Washington in New Hampshire, USA. It uses a Marsh rack system and one or two steam locomotives and six biodiesel powered locomotives to carry tourists to the top of the mountain. Its track is built to 4 ft 8 in (1,422 mm) gauge, which is technically a narrow gauge.

It is the second steepest rack railway in the world after the Pilatus railway, with an average grade of over 25% and a maximum grade of 37.41%. The railway is approximately 3 miles (4.8 km) long and ascends Mt. Washington's western slope beginning at an elevation of approximately 2,700 feet (820 m) above sea level and ending just short of the mountain's summit peak of 6,288 feet (1,917 m). The train ascends the mountain at 2.8 miles per hour (4.5 km/h) and descends at 4.6 mph (7.4 km/h). It takes approximately 65 minutes to ascend and 40 minutes to descend although the diesel can go up in as little as 37 minutes.

The construction reached the summit in July 1869. The early locomotives all had vertical boilers, like many stationary steam engines of the time. The boilers were mounted on trunnions allowing them to be held vertically no matter what the gradient of the track.