Not sure Dark Souls expanded their map and dungeon or not.
In DS1, the world is not as open and big as Skyrim, but the game won't restrict you much from going anywhere.

Also take note that DS is quite different from Skyrim in term of RPG elements.
Dark Souls don't have quests log/marker, only few NPCs, and provide limited explanation and guidance on storyline.
And the biggest difference, difficulty. 

It is a masterpiece but not for everyone.
Many peoples got the game due to reviews/recommendation, then sells/stop playing shortly afterwards, not even finish first dungeon/boss.
Better to try DS1 first if you are new to this series.