Springs have provided the inhabitants of the Judean Mountains with fresh water from ancient times until today. Ein Tzuba is a spring which provides water regularly, all year round. In ancient times it used to get blocked, but in King Herod's times a tunnel was dug from the fountainhead inside the hill out to the opening on the hill slope.
Today you can visit the spring and the tunnel; you climb down a steel ladder and then crawl (or walk in a crouched position) for about 100 meters in the dark to reach the fountainhead and the chamber built around it.
Outside there is a pleasant picnic site, with some ancient tombs at the background.
The best walking tour from Tzuba will lead you to the hill rising to the west of the kibbutz: Tel Tzuba. After a short climb you will see the remains of ancient walls and buildings, half covered by the vegetation. This is what's left of the Crusader castle of Belmont, constructed in the 12th century as part of the defense system around Jerusalem.
The castle actually stood almost intact until the 19th century. Then the castle became the refuge of Arabs who fled from the nearby village of Abu Gosh, a village of highwaymen in those days, which came under the attack of the forces of the Egyptian ruler, Ibrahim Pasha.
These refugees did not expect Ibrahim Pasha to use artillery fire against them, but that's exactly what he did. Cannon shelling turned the castle into rubble.
Today you can see a well preserved corner of the wall with part of the moat surrounding it, and some more ruins within the walls. Watch your step and stay on the path, as there are some open holes in the ground. Don't climb the ruins because of the danger of collapse.
The view from the hilltop is great, towards the northern part od the Jerusalem Mountains, Abu Gosh, Kiryat-Anavim, Ma'aleh-Ha-Hamisha, Har Adar and more.