diff --git a/common/prtfile.cc b/common/prtfile.cc
index 4cfcb784..57139437 100644
--- a/common/prtfile.cc
+++ b/common/prtfile.cc
@@ -24,6 +24,7 @@
 #include <common/bspfile.hh>
 
 #include <fstream>
+#include <fmt/ostream.h>
 
 constexpr const char *PORTALFILE = "PRT1";
 constexpr const char *PORTALFILE2 = "PRT2";
@@ -171,3 +172,28 @@ prtfile_t LoadPrtFile(const fs::path &name, const bspversion_t *loadversion)
 
     return result;
 }
+
+static void WriteDebugPortal(const polylib::winding_t &w, std::ofstream &portalFile)
+{
+    fmt::print(portalFile, "{} {} {} ", w.size(), 0, 0);
+    for (int i = 0; i < w.size(); i++) {
+        fmt::print(portalFile, "({} {} {}) ", w.at(i)[0], w.at(i)[1], w.at(i)[2]);
+    }
+    fmt::print(portalFile, "\n");
+}
+
+void WriteDebugPortals(const std::vector<polylib::winding_t> &portals, fs::path name)
+{
+    size_t portal_count = portals.size();
+
+    std::ofstream portal_file(name, std::ios_base::binary | std::ios_base::out);
+    if (!portal_file)
+        FError("Failed to open {}: {}", name, strerror(errno));
+
+    fmt::print(portal_file, "PRT1\n");
+    fmt::print(portal_file, "{}\n", 0);
+    fmt::print(portal_file, "{}\n", portal_count);
+    for (auto &p : portals) {
+        WriteDebugPortal(p, portal_file);
+    }
+}
diff --git a/include/common/aabb.hh b/include/common/aabb.hh
index 30372517..095aae63 100644
--- a/include/common/aabb.hh
+++ b/include/common/aabb.hh
@@ -228,6 +228,21 @@ public:
     auto stream_data() { return std::tie(m_corners); }
 };
 
+template<class V>
+inline std::array<qplane3<V>, 6> aabb_planes(const aabb<V, 3> &bbox)
+{
+    return {
+        qplane3<V>{qvec<V,3>( 1,0,0),  bbox.maxs()[0]},  // +X
+        qplane3<V>{qvec<V,3>(-1,0,0), -bbox.mins()[0]},  // -X
+
+        qplane3<V>{qvec<V,3>(0, 1,0),  bbox.maxs()[1]},  // +Y
+        qplane3<V>{qvec<V,3>(0,-1,0), -bbox.mins()[1]},  // -Y
+
+        qplane3<V>{qvec<V,3>(0,0, 1),  bbox.maxs()[2]},  // +Z
+        qplane3<V>{qvec<V,3>(0,0,-1), -bbox.mins()[2]},  // -Z
+    };
+}
+
 // Fmt support
 template<class T, size_t Dim>
 struct fmt::formatter<aabb<T, Dim>> : formatter<qvec<T, Dim>>
diff --git a/include/common/polylib.hh b/include/common/polylib.hh
index 3b70ec81..d85c4ca8 100644
--- a/include/common/polylib.hh
+++ b/include/common/polylib.hh
@@ -1321,6 +1321,33 @@ public:
     {
         return directional_equal(w, equal_epsilon) || directional_equal(w.flip(), equal_epsilon);
     }
+
+    static std::array<winding_base_t, 6> aabb_windings(const aabb3d &bbox) {
+        double worldextent = 0;
+        for (int i = 0; i < 3; ++i) {
+            worldextent = max(worldextent, abs(bbox.maxs()[i]));
+            worldextent = max(worldextent, abs(bbox.mins()[i]));
+        }
+        worldextent += 1;
+
+        std::array<winding_base_t, 6> result;
+        auto planes = aabb_planes(bbox);
+
+        for (int i = 0; i < 6; ++i) {
+            result[i] = winding_base_t::from_plane(planes[i], worldextent);
+        }
+
+        for (int i = 0; i < 6; ++i) {
+            for (int j = 0; j < 6; ++j) {
+                if (i == j)
+                    continue;
+
+                result[i] = *result[i].clip_back(planes[j]);
+            }
+        }
+
+        return result;
+    }
 };
 
 // the default amount of points to keep on stack
diff --git a/include/common/prtfile.hh b/include/common/prtfile.hh
index e3509141..3e4ce620 100644
--- a/include/common/prtfile.hh
+++ b/include/common/prtfile.hh
@@ -50,3 +50,4 @@ struct prtfile_t
 
 struct bspversion_t;
 prtfile_t LoadPrtFile(const fs::path &name, const bspversion_t *loadversion);
+void WriteDebugPortals(const std::vector<polylib::winding_t> &portals, fs::path name);
diff --git a/light/lightgrid.cc b/light/lightgrid.cc
index 291fe4cc..af26dc1e 100644
--- a/light/lightgrid.cc
+++ b/light/lightgrid.cc
@@ -32,6 +32,7 @@
 #include <common/log.hh>
 #include <common/bsputils.hh>
 #include <common/fs.hh>
+#include <common/prtfile.hh>
 #include <common/imglib.hh>
 #include <common/parallel.hh>
 
@@ -96,6 +97,10 @@ void LightGrid(bspdata_t *bspdata)
         ceil(world_size[2] / light_options.lightgrid_dist.value()[2])
     };
 
+    auto grid_index_to_world = [&](const qvec3i &index) -> qvec3f {
+        return grid_mins + (index * light_options.lightgrid_dist.value());
+    };
+
     std::vector<lightgrid_samples_t> grid_result;
     grid_result.resize(grid_size[0] * grid_size[1] * grid_size[2]);
 
@@ -414,6 +419,25 @@ void LightGrid(bspdata_t *bspdata)
         // build the root node
         const uint32_t root_node = build_octree(qvec3i{0,0,0}, grid_size, 0);
 
+        // visualize the leafs
+        {
+            std::vector<polylib::winding_t> windings;
+
+            for (auto &leaf : octree_leafs) {
+                auto leaf_world_mins = grid_index_to_world(leaf.mins);
+                auto leaf_world_maxs = grid_index_to_world(leaf.mins + leaf.size - qvec3i(1,1,1));
+
+                aabb3d bounds(leaf_world_mins, leaf_world_maxs);
+
+                auto bounds_windings = polylib::winding_t::aabb_windings(bounds);
+                for (auto &w : bounds_windings) {
+                    windings.push_back(std::move(w));
+                }
+            }
+
+            WriteDebugPortals(windings, fs::path(light_options.sourceMap).replace_extension(".octree.prt"));
+        }
+
         // stats
         int stored_cells = 0;
         for (auto &leaf : octree_leafs) {