Entry from the Land Of Giants is at P12. Dragons defend their lair in company with Gargoyles and Spit Spiders at P9. Cross the River by moving east from M9 to M13. At P12 the Minotaur Fountain restores your health and mana (handy!). Cross again from M13 to J14 and from J14 to I11. The SageCross Fountain at K9 also restores your health and mana but the only way out is along the River. There is a very hard fight against Werebears, Hellhounds and Were Minotaurs at L10. Pray they don't control you! Ditto at M7.
Then go by River from I11 to G11. A fight at F11 is all you find. Then back along the River to I11, then J14 and thence to G13. Hop round to G14 where Dragon Breath Fountain increases your attributes. Runes here say Past the platforms a tapestry you will find, Illuminate the moons with the spectrum of the Moon Prism, the rest is smeared with blood.
From F14 enter the river and swim to a teleport platform at I16 which takes you to B15. Here a brilliant tapestry depicting moons decorates the room. Use the Moon Prism and a door appears where the tapestry was. Walk through and north to C16, then along the River to B14, and then to A11 where you find the door to Voranti's Treasure.
This looks like a long passage but walls form behind you and there are some complex fights against gangs of baddies. At C7 a gnome thief tells you that you are very near the final battle with En-Li-Kil. The four Rainbow Gems will light your way to the infinite beyond when they are all placed. Red, yellow, green and blue are the rainbow colours. Have your boat when the gems are set and sail the rainbow to your destiny.
Once you have cleared this area (I assume the whole of River's End) return to the dwarf miner who gave you the Hidden Mine Key to receive the reward of 3 platinum bars - which, unfortunately, I had to leave behind as I was carrying too much!
But, onwards and upwards! Cross the river from C10 to G10. At G8 is a statue that appears capable of holding a gem. Remembering the order given earlier (red, yellow, green, blue), use the red gem. A beam of red arcs over the Ageless Void. Then move one location north and use the yellow, another north and use the green, then one north again and use the blue (this is at J8). A vibrant rainbow of colour forms. Use the boat. It floats out of your pack on a swirl of magic dust, intersects the Rainbow and bursts into blinding light. Once your eyes adjust, you see an enormous Golden Boat bedecked with the rarest jewels and finest carvings. A rainbow voyage across the Ageless Void awaits you to the west. Move over the platform to I6 and onto the boat. The Zephyr Wind blows a light breeze from the east and the boat sails across the rainbow. The Zephyr tells you that only the FlexSword can remain in your hands when you encounter the Wind Elemental. Destroy him and the way to En-Li-Kil's domain will be clear. You arrive at an island in the centre of the void, on Level 11: Island Of Eternity (and thence Level 12: The Unknown).