Amelia has always said that old trees know secrets that they don't tell anyone. That's why on that summer afternoon, when her younger brother Franek brought home a piece of an old map he had found in the library, she wasn't the least bit surprised. The map was decorated with a drawing of a huge tree with forked roots. They both immediately thought of the giant oak tree standing at the end of the park. That same day, armed with torches, notebooks and pockets full of sweets, they set off towards the old oak tree. There was no one else in the park, and the only sounds were the quiet chirping of sparrows and the rustling of leaves underfoot. When they reached the spot, they saw a soft blue glow around the oak tree. Franek, who always wanted to be an explorer, was the first to lean over the roots and push back a piece of moss. Beneath it, a wooden flap appeared with an engraved tree symbol exactly like the one on the map. Amelia's heart began to beat faster. Together they pulled the metal handle. The flap opened, revealing a staircase leading deep into the ground, lit by a flickering blue light. With each step, luminous signs reminiscent of ancient runes appeared beneath their feet. At the bottom of the stairs were two large stone gates covered in strange, pulsating patterns. There was a smell of dampness and something that resembled honey in the air. The gates swung open silently, as if inviting them inside. On the other side, they could hear the sound of water and a gentle ringing, as if someone was tapping crystals. Amelia exchanged a quick glance with Frank. - 'Shall we go in? - whispered the boy, and the echo repeated his question somewhere deep in the tunnel. Just then, a cloud of silvery sparks shot out from behind the gates, and a motionless hooded figure with strangely glowing eyes appeared before them. The brother and sister stood as if transfixed, trying to decide what to do....