@Kestrel 's excellent Millennium 3D modpack / scenario for Test of Time.
Original description below taken from his lost website:
https://web.archive.org/web/2008120...gpond.com/kestrel18/Favourites.htm#Millennium
The Millenium 3-D Modpack/Scenario
The Millennium 3-D Modpack scenario attempts (within the constraints of the Civ2 game) to explore the scientific
and cultural advances that occurred over the last thousand years of Human history
and the corresponding Diversity of Millennium Military Units that were enabled by those ideas and technologies.
It also simulates a 3D world allowing undersea (Deep Ocean) travel, tunnels and cities under
the Earth, Stratospheric travel and much more.
4 Realms ! . . . Linked Maps !

The Image above tries to illustrate the concept of the Modpack / Scenario
As such the Advances Tech Tree has been extensively modified
(and is supported by an updated, descriptive civilopedia).
Some of the new (to standard Civ2) advances include :
Magna Carta, Guild System, Diplomacy, Printing Press, Vaulted Arch, Renaissance,
Rationalism, Revolutionary Ideology, Nationalism, Telephone, Television,
Colour T.V., Semiconductors,
Medieval Warfare, Firearms, Bayonet & Inf. Drill, Breech Loading, Rifled Barrels,
Repeating Rifle, Assault Rifle, National Defense Plan, Elite Training, Rapid Deployment,
Sloped Armour, S.C.U.B.A., Advanced Composites, Modern Agriculture,
Adv. Food Handling, Tunnel Engineering,
Also some of the earlier unit slots (e.g. Warrior, Legion, Chariot etc.) have been
recycled to make way for more units that are in keeping with the period from
1000 A.D. to now.
Anyone familiar with my "3-D" or "Multiverse" Scenarios will find no great surprises
in the Collection of Millennium Units however, although there are more modern units
than in any of my previous efforts.
Again, this is really more a Scenario within a Modpack rather than a fully-fledged
"set-piece" scenario with a theme and a clearly defined set of objectives.
Players cannot "cheat" as was previously possible in the 3-D Scenario
and utilise Cruise and Nuclear missiles underground. (They are of course
still permitted to submerge to Deep Ocean when loaded onto submarines).
Also, the wonders have been reduced in scope and number,
making it harder to triumph utilising the classic Civ2 formula.
Scenario utilises 4 linked maps - Earth , Underground, Stratosphere, Undersea (Deep Ocean).
The 2 Included Scenarios concentrate on the advances that occurred from 1,000 A.D. to 2,000 A.D
(although the scenario does not end until around 2,100 A.D.) . One scenario is set on a random map
whilst the other is set on a "Europe-like" map.
I have attempted to recycle as many of the Fantasy & Scifi sprites that
is feasible given that the sprite has to 'fit' into the reality context I am striving for.
Hide your Submarines in the deep ocean with their cargo of deadly missiles
and only rise to the surface to wreak havoc on the enemy !
Lay Sea-Mines in your strategic waterways to deter enemy shipping !
Tunnel under Enemy fortifications to undermine their defensive perimeter
or tunnel under the continental shelf to link up islands and move troops
from island to island without the need for a navy !
Build underground cities in Tunnels under the Earth's surface !
Soar over that ring of defensive pikemen or airnbases in your Stratospheric
aircraft or wreak havoc from the stratosphere with your Nuclear Missiles !

Pictured in the Screen shot of the Underworld above are :
- the Submarine unit,
- the Sea-Mine unit, &
- the Tunnelling Unit
Also various terrain examples
including : Deep Ocean,
Continental Shelf, Clay,
Bedrock and Tunnels.
The Millennium Modpack also includes a different variant of my Lighter Earth Terrain
Original description below taken from his lost website:
https://web.archive.org/web/2008120...gpond.com/kestrel18/Favourites.htm#Millennium
The Millenium 3-D Modpack/Scenario
The Millennium 3-D Modpack scenario attempts (within the constraints of the Civ2 game) to explore the scientific
and cultural advances that occurred over the last thousand years of Human history
and the corresponding Diversity of Millennium Military Units that were enabled by those ideas and technologies.
It also simulates a 3D world allowing undersea (Deep Ocean) travel, tunnels and cities under
the Earth, Stratospheric travel and much more.
4 Realms ! . . . Linked Maps !

The Image above tries to illustrate the concept of the Modpack / Scenario
As such the Advances Tech Tree has been extensively modified
(and is supported by an updated, descriptive civilopedia).
Some of the new (to standard Civ2) advances include :
Magna Carta, Guild System, Diplomacy, Printing Press, Vaulted Arch, Renaissance,
Rationalism, Revolutionary Ideology, Nationalism, Telephone, Television,
Colour T.V., Semiconductors,
Medieval Warfare, Firearms, Bayonet & Inf. Drill, Breech Loading, Rifled Barrels,
Repeating Rifle, Assault Rifle, National Defense Plan, Elite Training, Rapid Deployment,
Sloped Armour, S.C.U.B.A., Advanced Composites, Modern Agriculture,
Adv. Food Handling, Tunnel Engineering,
Also some of the earlier unit slots (e.g. Warrior, Legion, Chariot etc.) have been
recycled to make way for more units that are in keeping with the period from
1000 A.D. to now.
Anyone familiar with my "3-D" or "Multiverse" Scenarios will find no great surprises
in the Collection of Millennium Units however, although there are more modern units
than in any of my previous efforts.
Again, this is really more a Scenario within a Modpack rather than a fully-fledged
"set-piece" scenario with a theme and a clearly defined set of objectives.
Players cannot "cheat" as was previously possible in the 3-D Scenario
and utilise Cruise and Nuclear missiles underground. (They are of course
still permitted to submerge to Deep Ocean when loaded onto submarines).
Also, the wonders have been reduced in scope and number,
making it harder to triumph utilising the classic Civ2 formula.
Scenario utilises 4 linked maps - Earth , Underground, Stratosphere, Undersea (Deep Ocean).

The 2 Included Scenarios concentrate on the advances that occurred from 1,000 A.D. to 2,000 A.D
(although the scenario does not end until around 2,100 A.D.) . One scenario is set on a random map
whilst the other is set on a "Europe-like" map.
I have attempted to recycle as many of the Fantasy & Scifi sprites that
is feasible given that the sprite has to 'fit' into the reality context I am striving for.
Hide your Submarines in the deep ocean with their cargo of deadly missiles
and only rise to the surface to wreak havoc on the enemy !
Lay Sea-Mines in your strategic waterways to deter enemy shipping !
Tunnel under Enemy fortifications to undermine their defensive perimeter
or tunnel under the continental shelf to link up islands and move troops
from island to island without the need for a navy !
Build underground cities in Tunnels under the Earth's surface !
Soar over that ring of defensive pikemen or airnbases in your Stratospheric
aircraft or wreak havoc from the stratosphere with your Nuclear Missiles !

Pictured in the Screen shot of the Underworld above are :
- the Submarine unit,
- the Sea-Mine unit, &
- the Tunnelling Unit
Also various terrain examples
including : Deep Ocean,
Continental Shelf, Clay,
Bedrock and Tunnels.
The Millennium Modpack also includes a different variant of my Lighter Earth Terrain