Representing a 2D array as a 1D array with wrapping sides (up at top of 1st column will place you bottom of 1st column)

TileManager.cs

using UnityEngine;
using System.Collections;

public class TileManager : MonoBehaviour
{
    public GameObject walkableTile;
    public GameObject blockingTile;

    private GameObject[] tiles = new GameObject[25];
    public int offset = 0; // current position on grid array

    public enum Direction
    {
        Up = 1,
        Down = -1,
        Left = 5,
        Right = -5
    }

    void Start()
    {
        InstantiateArrayTiles();
    }

    void Update()
    {
        if (Input.GetKeyDown(KeyCode.LeftArrow))
        {
            GetTile(Direction.Left);
        }
        else if (Input.GetKeyDown(KeyCode.RightArrow))
        {
            GetTile(Direction.Right);
        }
        else if (Input.GetKeyDown(KeyCode.UpArrow))
        {
            GetTile(Direction.Up);
        }
        else if (Input.GetKeyDown(KeyCode.DownArrow))
        {
            GetTile(Direction.Down);
        }
    }

    private void InstantiateArrayTiles()
    {
        for (int i = 0; i < 5; i++)
        {
            for (int j = 0; j < 5; j++)
            {
                GameObject tile = Instantiate(walkableTile, new Vector2(1.1f * i, 1.1f * j), Quaternion.identity) as GameObject;
                tile.transform.parent = transform;
                tile.name = ((i * 5) + j).ToString();
                tiles[(i * 5) + j] = tile;
            }
        }
        transform.position = new Vector2(-2.2f, -2.2f);
    }

    private GameObject GetTile(Direction dir)
    {
        if (dir == Direction.Left || dir == Direction.Right)
        {
            offset += (int)dir;
            int x = Mod(offset, 25);
            return tiles[x];
        }
        else
        {
            // 4 9 14 19 24
            // 3 8 13 18 23
            // 2 7 12 17 22
            // 1 6 11 16 21
            // 0 5 10 15 20
            
            // get current column position (0 - 4)
            int a = Mod(offset, 25);
            int currentCol = (int)Mathf.Floor(a / 5);

            offset += (int)dir;          // move current position in direction 
            int newRow = Mod(offset, 5); // get vertical position in column (0 - 4)

            // set our current position to proper 'next' tile 
            offset = (currentCol * 5) + newRow;
            return tiles[offset];
        }
    }

    // C# doesn't have modulus so lets write our own
    private int Mod(int a, int b)
    {
        int x = a % b;
        if (x < 0) x += b;
        return x;
    }
}