This is a utility for converting HoMM3 maps into Olden Era maps. Includes support for many types of events and most types of objects that have a parallel in Olden Era.

– This is a fail open program, meaning the tool will let you try to do something impossible with a warning (usually meaning an object will not appear in the resulting Olden Era map).
– Oceans are turned into sand terrain at a low elevation. This provides the best future support for ocean travel if it is ever added, as Olden Era water is placed by adding water to low-elevation terrain.

– Underground is simulated by increasing the map size and having two separate regions connected by portals

– Map dimensions are not compatible between these two games, so the outside of a map is padded with elevated cliff terrain. This may or may not be good enough for purposes of your scenario, in which case you might want to add obstacles to hard-block movement or turn those areas into unreachable zones so map spells cannot access them.