Never got it to work -> sprites and walls

If you are using characters for walls you can check the video memory directly with:

VPEEK(&H1800+INT(Y/8)*32+INT(X/8))

It will return the number of the character you have at position X,Y

You can just have a copy of your map on RAM. Then check bytes (mostly like Rogerup said, but using RAM instead of VRAM, just PEEK). Using RAM is way faster. But... you need space on RAM Wich in Basic is also a treasure...

So think what do you need more. RAM Space or Game Speed?

What I have done for MSX2 is a simple tile based representation of your maze, divide your screen up in blocks of 8x8 or 16x16, whatever your tile-size is and use a 1 for something inpenetrable, and a 0 for something that you can walk through, a 2 for a ladder, 3 for a trap etc.
Then you translate your x,y coordinate from your sprite to your map-coordinates (divide by 8 or 16, depending on tile-size). This then gives you the spot in your map to look for a 1 or 0. If you want to account for a moving sprite, then you check the position x+8 for moves to the right, x-8 for moves to the left etc. before you move your sprite to see if you can.
For MSX1 it is similar: If you are using screen 1, then you already are using a character based map in VRAM, you then just need the character code for whatever is a wall or trap or stairs or ladder or lava-wall to take action upon.

A tile map based representation of the world is the most standard approach, using a 2-dimensional array (or 1-dimensional with y * width + x) with bytes representing 8x8 or 16x16 tiles.

Then to do collision detection, if the character sprite moves right, calculate the tile(s) that corresponds to the top right and bottom right pixel of the sprite, and check if the tile is solid or not. The simplest way is to say tiles with index 0-127 are pass-through, and tiles 128-255 are solid. A more complex set-up is to have a separate table which specifies for each tile index whether it is solid or not.

If you search Google or Youtube for something like “tile map” or “tile map basics” you should be able to find a number of deeper explanations of the concept, maybe that will be useful. They will not likely be specific to MSX, but still give you useful background information. Many games from the 80s were based on this concept (e.g. super mario), and many are even today.

In the MSX pattern screen modes (screen 1, 2 and 4), they are already tile based modes using 8x8 tiles, so there you could even check the tile number by reading from VRAM, rather than to do your lookups in a separate tile map in RAM. To use the pattern modes as a tile map, you would typically not use commands like line, pset, etc., rather you would draw a tile map in a graphics editor, load it as pattern and colour table data, and then vpoke the tile numbers into the name table.

What is the problem exactly, Latok? Can you make a more precise question? That alone usually already helps you