I was experimenting with seeds to create worlds where I can have embarks overlapping multiple biomes (save, preferably both good and evil) and multiple neighbour civs.
Result is below, a very nice world, but there are few things to do:
[WORLD_GEN]
[TITLE:MEDIUMooo]
[SEED:NnuaosumFqotYx9cy2zR]
[DIM:129:129]
[EMBARK_POINTS:80000]
[END_YEAR:200]
[BEAST_END_YEAR:200:0]
[REVEAL_ALL_HISTORY:1]
[CULL_HISTORICAL_FIGURES:1]
[ELEVATION:25:400:401:201]
[RAINFALL:0:75:401:401]
[TEMPERATURE:20:60:201:201]
[DRAINAGE:0:100:401:401]
[VOLCANISM:0:100:201:201]
[SAVAGERY:20:100:3200:3200]
[ELEVATION_FREQUENCY:2:5:4:1:1:2]
[RAIN_FREQUENCY:2:30:5:0:1:1]
[DRAINAGE_FREQUENCY:2:5:1:5:1:5]
[TEMPERATURE_FREQUENCY:2:0:5:5:5:0]
[SAVAGERY_FREQUENCY:2:30:1:1:1:67]
[VOLCANISM_FREQUENCY:1:1:1:1:2:3]
[POLE:NORTH_OR_SOUTH]
[MINERAL_SCARCITY:500]
[MEGABEAST_CAP:40]
[SEMIMEGABEAST_CAP:60]
[TITAN_NUMBER:60]
[TITAN_ATTACK_TRIGGER:60:0:400000]
[DEMON_NUMBER:10]
[NIGHT_TROLL_NUMBER:14]
[BOGEYMAN_NUMBER:2]
[VAMPIRE_NUMBER:26]
[WEREBEAST_NUMBER:14]
[SECRET_NUMBER:28]
[REGIONAL_INTERACTION_NUMBER:4]
[DISTURBANCE_INTERACTION_NUMBER:14]
[EVIL_CLOUD_NUMBER:8]
[EVIL_RAIN_NUMBER:8]
[GENERATE_DIVINE_MATERIALS:1]
[GOOD_SQ_COUNTS:2048:512:1]
[EVIL_SQ_COUNTS:2048:512:1]
[PEAK_NUMBER_MIN:0]
[PARTIAL_OCEAN_EDGE_MIN:0]
[COMPLETE_OCEAN_EDGE_MIN:0]
[VOLCANO_MIN:0]
[REGION_COUNTS:SWAMP:0:0:0]
[REGION_COUNTS:DESERT:0:0:0]
[REGION_COUNTS:FOREST:0:0:0]
[REGION_COUNTS:MOUNTAINS:0:0:0]
[REGION_COUNTS:OCEAN:0:0:0]
[REGION_COUNTS:GLACIER:0:0:0]
[REGION_COUNTS:TUNDRA:0:0:0]
[REGION_COUNTS:GRASSLAND:0:0:0]
[REGION_COUNTS:HILLS:0:0:0]
[EROSION_CYCLE_COUNT:250]
[RIVER_MINS:5:10]
[PERIODICALLY_ERODE_EXTREMES:1]
[OROGRAPHIC_PRECIPITATION:1]
[SUBREGION_MAX:5000]
[CAVERN_LAYER_COUNT:3]
[CAVERN_LAYER_OPENNESS_MIN:75]
[CAVERN_LAYER_OPENNESS_MAX:100]
[CAVERN_LAYER_PASSAGE_DENSITY_MIN:0]
[CAVERN_LAYER_PASSAGE_DENSITY_MAX:25]
[CAVERN_LAYER_WATER_MIN:0]
[CAVERN_LAYER_WATER_MAX:25]
[HAVE_BOTTOM_LAYER_1:1]
[HAVE_BOTTOM_LAYER_2:1]
[LEVELS_ABOVE_GROUND:5]
[LEVELS_ABOVE_LAYER_1:17]
[LEVELS_ABOVE_LAYER_2:2]
[LEVELS_ABOVE_LAYER_3:2]
[LEVELS_ABOVE_LAYER_4:2]
[LEVELS_ABOVE_LAYER_5:2]
[LEVELS_AT_BOTTOM:1]
[CAVE_MIN_SIZE:5]
[CAVE_MAX_SIZE:25]
[MOUNTAIN_CAVE_MIN:10]
[NON_MOUNTAIN_CAVE_MIN:15]
[ALL_CAVES_VISIBLE:1]
[SHOW_EMBARK_TUNNEL:2]
[TOTAL_CIV_NUMBER:30]
[TOTAL_CIV_POPULATION:15000]
[SITE_CAP:300]
[PLAYABLE_CIVILIZATION_REQUIRED:1]
[ELEVATION_RANGES:8:8:4]
[RAIN_RANGES:8:4:4]
[DRAINAGE_RANGES:4:4:8]
[SAVAGERY_RANGES:32:1:64]
[VOLCANISM_RANGES:8:8:8]
If you want elves to survive, you need to mod their entity file to
[START_BIOME:ANY_FOREST]
[START_BIOME:ANY_SHRUBLAND]
[BIOME_SUPPORT:ANY_LAKE:1]
[BIOME_SUPPORT:ANY_FOREST:2]
[BIOME_SUPPORT:ANY_RIVER:1]
[BIOME_SUPPORT:ANY_SHRUBLAND:2]
Otherwise they will be wiped out.
If you want dwarves to survive, same thing add them grasslands/deserts etc.
(however how well dwarves fare is somehow tied to how well elves and humans prosper. with no elves there will be often no dwarves left standing. must be trade or something.)
The thing is, orcs and other civs will be moving onto them very often. Also, kobolds and goblins tend to not survive no matter what.
The settings above allow to create a world, where there will be embarks with 8 neighbouring civs, one or two towers, savage evil/good biomes next to each other, river etc.
Have fun