For version 2.01 onwards you will also need to install Roughly Enough IDs (whose modid is "jeid" and which is an update of Just Enough IDs).
This is the Ordovician dimension. The portal block needed to get here and the biomes included are listed below. To open a portal click on it with the bone wand, which has been enchanted with the Enchantment of Time Reversal. The Enchantment of Time Reversal can be obtained from a Palaeobotanist villager, or as a rare chance on the crafting table. Note that the biomes in these dimensions are able to be extremely large, up to several thousand blocks across. Travelling 10 blocks in the overworld will move you 100 in a custom dimension though, and the main mod's config has an option to allow you to increase that if you felt the need. There are achievements for finding all biomes (biomes listed on the same line are regarded as equally valid for those achievements):
Ordovician: Portal block: Coral reef block - hint you need something sticky to hold falling blocks in place
- Ordovician Frozen Beach
- Ordovician Algal Reef
- Ordovician Barren Land
- Ordovician Beach
- Ordovician Bog
- Ordovician Bryozoan Reef
- Ordovician Craggy Wastes
- Ordovician Frozen Jagged Wastes
- Ordovician Frozen Land
- Ordovician Frozen Ocean
- Ordovician Frozen Shallow Ocean
- Ordovician Hilly Wastes
- Ordovician Icebergs
- Ordovician Icy Crevasse
- Ordovician Lagoons
- Ordovician Ocean
- Ordovician Shallow Ocean
- Ordovician Sponge Forest