There are 9 maps to beat and the next map only opens after you have defeated the one before.
The Arcane Portal is located in the sea near your town and glows purple when it is open.
The Arcane portal doesn't cost energy, but requires 8 hours to open again.
Each level has a set of masteries and skill which tremedously helps beating it. For example the first map cannot be beaten with 18 lvl40 heroes, but it can be beaten with almost the same setup and the Disarm bonus of the hero Mystic.
Besides the listed bonuses, Arcane Portel offers a way to level up heroes. Map 1 gives 12600xp, which is enough to level a hero to lvl23. Map2 offers 15300xp which is enough for lvl27. It is also useful for XP Guild Quests.
Map 1 - Path of Skulls Edit
Oggmar Grimefest (Horde)
Possible Rewards 1200 Soul Shards, 25 Energy, 25 Siege Stones, 1 Gold Key, 15 Rare Soul Stone, 3 Epic Soul Stones, 25 Gems, 5 Ring Relic, 5 Rune Relic, 1 Mythic Soul Stone, Swiftwing, Templar
Skills to help: Freezing, Ghost Arrow
Masteries to help - Disarm (Mystic), Horde
Typical level required to beat - ??
Notes - Templar is useful for, but not required for level 95 of Tree of Life.
Map 2 - Lava Slope Edit
Molten Goliath (Demon)
Possible Rewards 1800 Soul Shards, 35 Energy, 35 Siege Stones, 2 Gold Key, 25 Rare Soul Stone, 5 Epic Soul Stones, 35 Gems, 6 Ring Relic, 6 Rune Relic, 1 Mythic Soul Stone, Helmed Horrors, Giant Killer
Skills to help: Dispel, Healing Light, Cleansing, Shield Explosion
Masteries to help: Calm (Legionnaire), Demon
Typical level required to beat - With Calm, Demon and Cleansing bonus sum lvl of 672 results 1 dead.
Map 3 - Edge of the Abyss Edit
Wyrm the Insane (Sylvan)
Possible Rewards 2500 Soul Shards, 50 Energy, 50 Siege Stones, 3 Gold Key, 30 Rare Soul Stone, 7 Epic Soul Stones, 50 Gems, 7 Ring Relic, 7 Rune Relic, 1 Mythic Soul Stone, Chaos Master, Shaman
Skills to help: Seal Break, Shield Split, Bonus Maker (Healing), Bonus Maker (Bow)
Masteries to help: Great Reaction (Rifleman), Sylvan
Typical level required to beat - With every bonus except the potion maker and sum lvl of 742 results 1 dead. With the same setup, but without Great Reaction and sum lvl of 889, died at boss.