Huge linden tree - what to grow under it?

I have just became an owner of a property where a huge, old linden tree stands proudly in a vicinity of the house. The soil around the trunk is barren, in a sense that nothing grows there. The ground around the tree goes slightly up towards tree trunk. The trunk itself is well over 1 meter in diameter at knee level. Further from a trunk, but still under umbrella of branches a weak grass grows in sandy soil. I would love to create a sort of a plant guild to grow under this magnificent tree, but have no idea what could be grown there. I assume, the first step is to mulch the barren soil heavily, perhaps also add some compost etc. I would appreciate your advice since I have no experience whatsoever in this field.

It would help to know where you are. I have an American Basswood in our yard . Below it is an old lilac that has lived out it's days , wild thimbleberries , daffodils and barenaked-ladies. I have read that ginseng , golden seal , black cohosh likes to grow below Basswood also.

Thanks, I live in Europe, Poland, near city of Warsaw, european hardiness zone 6

Most temperate climates have a cadre of woodland ephemerals and groundcovers, many of them useful and medicinal. Not sure which ones are native or adapted to your zone, some research will elucidate this. Ginseng is one of the most valuable, but also among the most picky....might be better to start with something more adaptable and prove that they can work. I'm surprised there is no leaf litter under the tree....do linden leaves decay that quickly or have they been removed? Perhaps a season's observation will determine this, and also if any plants come up from hidden bulbs/roots/seeds as the spring and summer come in. If the linden leaves disappear of themselves you may need to import some more decay-resistant mulch to get the understory plants started.
If you can reach any of them, young linden leaves are quite edible!

Linden leaves were mostly blown away from under the tree by the wind carrying them all across the yard. Then they were removed every autumn. I'm sure nothing comes from bulbs or roots in a vicinity of tree trunk, except of young linden shoots. I know that there were some attempts to grow some flowers from bulbs there (like snowdrops) but no luck. Yes, some branches are reachable, I must try those leaves this spring.