Ajahn Dhammasiha explains suitable meditation objects for investigation (vipassana/insight/wisdom) that we can direct our attention to, after the mind emerges from Samatha/Samādhi meditation.

Samādhi/Concentration imbues the mind with calm, tranquillity, hightened mindfulness, brightness and radiant awareness, as well as wholesome joy, rapture and bliss. At the same time, the five hindrances of sensual desire, aversion, laziness, restlessness and doubt are suppressed (or at least reduced).

Of course, all these things are desirable and very pleasant to experience in and by themselves. However, even more important is that they provide the conditions for profound insight to arise. Whenever our mind has developed a certain level of calm/samatha, we should these mental qualities to develop insight/vispassana.

We're not merely enjoying the bright and blissful qualities of samādhi, we're using them to do the work of developing wisdom, to see things as they really are (yathā-bhūta-ñāṇadassana), to investigate and analyse.

So what are the areas of investigation the Buddha recommended for that purpose?

And how are we to investigate them, in which way should we contemplate them?

In this reflection, Ajahn Dhammasiha talks about the 5 groups of clinging (pañcupādānakkhandhā) as suitable objects for profound insight contemplation:

Rūpa = Form
Vedanā = Feeling (pleasant of unpleasant of neutral)
Saññā = Perception (Recognizing, labelling)
Sankhārā = Mental formations, in particular intention (cetana) & thinking (vitakka)
Viññāṇa = Consciousness

Ajahn also mentions the four foundations of mindfulness, which are highly suitable meditation objects for developing insight as well, and which tend to be easier to contemplate than the 5 groups of clinging.

How to Develop Vipassana after Samadhi | 5 Groups of Clinging vs 4 Foundations of Mindfulness | Ajahn Dhammasiha