Most accessible field for undergraduate independent research

Question

I am studying in Europe as a mathematics undergraduate and I would like to start my own independent research in pure mathematics. I do not expect to find a field in which I would be able to prove new results using only the limited knowledge acquired from the lectures I have attended; none the less I suspect that some fields would require more backround knowledge than others, for example I have read multiple posts from students interested in number theory with answers that point out the great gap between the theoretical background needed to tackle the subject at the collage level and reasearch level. I am genuinely interested in solving problems just for the fun of it, so I think that my best option is to simply find a field with relatively light prerequisites and start from some non-famous open problems there. The point of this whole endeavour is to familiarize myself with the research process, not necessarily contribute to it; that would be a nice bonus. To wrap it up, I would like some suggestions regarding the field to pick - the one you think is most accessible to undegraduate students.