Функция Physics.ClosestPoint

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using UnityEngine;
 
public class GameManager : MonoBehaviour
{
    [SerializeField] float moivingSpeed = 0.01f;
    [SerializeField] List<Rigidbody> stones = new List<Rigidbody>();
    [SerializeField] List<Rigidbody> tower = new List<Rigidbody>();
 
    void Update()
    {
        if (Input.GetMouseButtonDown(0))
        {
            //find stone under mouse
            var ray = Camera.main.ScreenPointToRay(Input.mousePosition);
            if (Physics.Raycast(ray, out var hit))
            {
                if (stones.Contains(hit.rigidbody))//is free stone?
                    OnStonePicked(hit.rigidbody);
            }
        }
    }
 
    private async void OnStonePicked(Rigidbody stone)
    {
        //make animation
        await MoveToTower(stone);
        //remove from stone list
        stones.Remove(stone);
        //add to tower list
        tower.Add(stone);
        //is tower completed? => enable tower physics
        if (stones.Count == 0)
        foreach (var s in tower)
            s.isKinematic = false;
    }
 
    private async Task MoveToTower(Rigidbody stone)
    {
        //find bounding box of last stone in tower
        var towerBox = tower.Last().GetComponent<Collider>().bounds;
        //my bounding box
        var box = stone.GetComponent<Collider>().bounds;
        var offset = box.center - stone.position;//ofsset of collider center relative to transform center
        //calc target point
        var targetPos = towerBox.center + (towerBox.extents.y + box.extents.y) * Vector3.up;
        //move me up to tower
        for (float i = 0; i <= 1; i += moivingSpeed)
        {
            stone.position = Vector3.Lerp(box.center, targetPos, i) - offset;
            await Task.Delay(5);
        }
        //adjust position accurately
        stone.position = targetPos - offset;
    }
}